AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON OCTOBER 24, 2001
                                         Registration Statement No.  _________



                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                    FORM S-8

                             Registration Statement
                                    Under The
                             Securities Act Of 1933


                               AMEREN CORPORATION
             (Exact name of registrant as specified in its charter)


    State of Missouri                                       43-1723446
  (State or other jurisdiction                            (IRS Employer
of incorporation or organization)                       Identification No.)


                              1901 Chouteau Avenue
                            St. Louis, Missouri 63103
          (Address, including zip code, of principal executive offices)
                    -----------------------------------------

                   Ameren Corporation Savings Investment Plan
     (formerly known as the Union Electric Company Savings Investment Plan)
                            (Full title of the plan)

                WARNER L. BAXTER, Senior Vice President, Finance
        STEVEN R. SULLIVAN, Vice President, General Counsel and Secretary
                 1901 Chouteau Avenue, St. Louis, Missouri 63103
                                 (314) 621-3222
(Names, address and telephone number, including area code,of agents for service)




                         CALCULATION OF REGISTRATION FEE
============================================================================================================================
                                                                       Proposed
                                                    Amount             maximum         Proposed maximum       Amount of
                Title of securities                  to be          offering price         aggregate         registration
                 to be registered              registered(1)(2)      per share(3)       offering price          fee(2)
----------------------------------------------------------------------------------------------------------------------------
                                                                                                 
     Common Stock, $.01 par value,
      including related plan interests -
      Ameren Corporation Savings Investment
      Plan                                     3,000,000 shares         $39.57           $118,710,000          $29,678
============================================================================================================================

  (1) In addition, pursuant to Rule 416(c) under the Securities Act of 1933,
      this Registration Statement also covers an indeterminate amount of
      interests to be offered or sold pursuant to the employee benefit plan
      described herein.
  (2) The shares being registered are in addition to 2,600,000 shares (of which
      approximately 609,000 shares are unsold), including related plan
      interests, currently registered (Form S-8, Registration Statement
      No. 333-43737) for offer and sale pursuant to the employee benefit plan
      described herein. Pursuant to Rule 457(h) and General Instruction E of
      Form S-8, the filing fee is paid with respect to the additional shares
      only.
  (3) Calculated in accordance with Rule 457(h) on the basis of the average
      of the high and low prices of Ameren Corporation Common Stock as reported
      on the New York Stock Exchange Composite Tape on October 22, 2001.


-------------------------------------------------------------------------------
                                                           Page 1 of 9 pages
                                          Exhibit Index is located on page II-5




         Registration of Additional Securities; Incorporation by Reference. This
Registration Statement registers additional securities of the same class as
other securities for which a Registration Statement filed on this Form relating
to the Ameren Corporation Savings Investment Plan (formerly known as the Union
Electric Company Savings Investment Plan) is effective. The contents of such
earlier Registration Statement (Form S-8, Registration Statement No. 33-43737)
are hereby incorporated by reference in this Registration Statement, except that
Items 3, 5 and 8 shall read as follows:

Item 3.  Incorporation of Documents by Reference

         The following documents, previously filed with the Securities and
Exchange Commission by Ameren Corporation (the "Company") (File No. 1-14756) and
the Ameren Corporation Savings Investment Plan (the "Plan") pursuant to the
Securities Exchange Act of 1934, are incorporated by reference in this
Registration Statement:

         1. Annual Report on Form 10-K of the Company for the fiscal year ended
            December 31, 2000.

         2. Quarterly Reports on Form 10-Q of the Company for the quarters ended
            March 31 and June 30, 2001.

         3. Current Reports on Form 8-K of the Company dated January 11, May 17
            and July 2, 2001.

         4. The  description of the Common Stock of the Company included  under
            the caption "Description of Holdings  Capital Stock" in the
            Registration Statement on Form S-4 of the Company
            (Reg. No. 33-64165) filed November 13, 1995.

         5. The Annual Report on Form 11-K of the Plan for the fiscal year ended
            December 31, 2000.

All documents subsequently filed by the Company or the Plan pursuant to Sections
13(a), 13(c), 14 and 15(d) of the Securities Exchange Act of 1934, prior to the
filing of a post-effective amendment which indicates that all securities offered
have been sold or which deregisters all securities then remaining unsold, shall
be deemed to be incorporated by reference in this Registration Statement and to
be a part hereof from the date of filing of such documents.

Item 5.  Interests of Named Experts and Counsel

         Steven R. Sullivan, Vice President, General Counsel and Secretary of
the Company, will opine as to the legality of the shares of Common Stock of the
Company and Plan interests to be issued under the Plan. Mr. Sullivan is eligible
to participate in the Plan.

Item 8.  Exhibits

         Exhibit No.
         ----------

         *4.1   Restated Articles of Incorporation of the Company
                (File No. 33-64165, Annex F).
         *4.2   Certificate  of  Amendment  to the  Restated  Articles  of
                Incorporation  filed with the Secretary of State of the State
                of Missouri on December 14, 1998 (1998 Form 10-K, Exhibit 3(i)).
         *4.3   By-Laws of the Company as amended to December 31, 1997 (1997
                Form 10-K, Exhibit 3(ii)).
          5     Opinion re legality.
                The Company hereby undertakes that it has submitted
                the Plan and will submit any amendment thereto to the
                Internal Revenue Service in a timely manner and has made or will
                make all changes required by the Internal Revenue Service in
                order to qualify the Plan.

                                      II-1



         23.1   Consents of Independent Accountants.
         23.2   Consent of Counsel (included in Exhibit 5).
         24     Powers of Attorney.

         -----------
         *Incorporated herein by reference.


                                      II-2



                                   SIGNATURES

          The Registrant. Pursuant to the requirements of the Securities Act of
1933, the Registrant certifies that it has reasonable grounds to believe that it
meets all of the requirements for filing on Form S-8 and has duly caused this
Registration Statement to be signed on its behalf by the undersigned, thereunto
duly authorized, in the City of St. Louis, State of Missouri, on October 24,
2001.

                                              AMEREN CORPORATION


                                             By   /s/Warner L. Baxter
                                               ------------------------
                                                     WARNER L. BAXTER
                                             Senior Vice President, Finance


         Pursuant to the requirements of the Securities Act of 1933, this
Registration Statement has been signed by the following persons in the
capacities and on the date above indicated.

        Signature                                           Title
                                                  Chairman, President and Chief
    /s/ Charles W. Mueller                        Executive Officer and Director
   --------------------------                     (Principal Executive Officer)
        CHARLES W. MUELLER


   /s/ Warner L. Baxter                          Senior Vice President, Finance
  ---------------------------
       WARNER L. BAXTER                           (Principal Financial Officer)

   /s/ Martin J. Lyons                                       Controller
  ---------------------------
       MARTIN J. LYONS                           (Principal Accounting Officer)

   /s/ William E. Cornelius*                      /s/ John Peters MacCarthy*
  ---------------------------                  --------------------------------
  WILLIAM E. CORNELIUS, Director                JOHN PETERS MACCARTHY, Director

   /s/ Clifford L. Greenwalt*                     /s/ Hanne M. Merriman*
  ---------------------------                  --------------------------------
  CLIFFORD L. GREENWALT, Director                 HANNE M. MERRIMAN, Director

   /s/ Paul L. Miller, Jr.*
  ---------------------------                  --------------------------------
  THOMAS A. HAYS, Director                       PAUL L. MILLER, JR., Director

                                                  /s/ Harvey Saligman*
  ---------------------------                  --------------------------------
  THOMAS H. JACOBSEN, Director                   HARVEY SALIGMAN, Director

   /s/ Richard A. Liddy*
  ---------------------------                  --------------------------------
  RICHARD A. LIDDY, Director                     JANET MCAFEE WEAKLEY, Director

                                                  /s/ James W. Wogsland*
  ---------------------------                  --------------------------------
  GORDON R. LOHMAN, Director                        JAMES W. WOGSLAND, Director


  ---------------------------
  RICHARD A. LUMPKIN, Director
                                              *By    /s/ Steven R. Sullivan
                                                 -----------------------------
                                                         STEVEN R. SULLIVAN
                                                          Attorney-In-Fact

                                      II-3





       The Plan. Pursuant to the requirements of the Securities Act of 1933, the
persons who administer the undersigned employee benefit plan have duly caused
this Registration Statement to be signed on their behalf by the undersigned
thereunto duly authorized, in the City of St. Louis, State of Missouri, on
October 24, 2001.


                                    AMEREN CORPORATION SAVINGS INVESTMENT PLAN



                                        By    /s/Warner L. Baxter
                                          ----------------------------
                                                 WARNER L. BAXTER
                                         Senior Vice President, Finance
                                              Ameren Corporation



                                      II-4






                                  EXHIBIT INDEX




 Exhibit No.
 -----------
    *4.1       Restated  Articles of  Incorporation  of  the Company
               (File No.  33-64165,  Annex F).

    *4.2       Certificate of Amendment to the Restated Articles of
               Incorporation filed  with  the  Secretary  of State of the State
               of Missouri  on  December  14, 1998 (1998 Form 10-K,
               Exhibit 3(i)).

    *4.3       By-Laws  of the  Company  as  amended to December   31,  1997
               (1997  Form  10-K, Exhibit 3(ii)).

     5         Opinion re legality.

    23.1       Consents of Independent Accountants.

    23.2       Consent of Counsel  (included in Exhibit 5).

    24         Powers of Attorney.
 ---------------
 *Incorporated herein by reference.


                                      II-5







                                                                   EXHIBIT 5

                                October 24, 2001



Ameren Corporation
1901 Chouteau Avenue
St. Louis, Missouri  63103

         Re:      Registration Statement on Form S-8 Relating to 3,000,000
                  Additional Shares of Common Stock, Including Related Plan
                  Interests

Ladies and Gentlemen:

         I have examined the Registration Statement on Form S-8 (the
"Registration Statement") filed by Ameren Corporation, a Missouri corporation
(the "Company"), with the Securities and Exchange Commission on October 24, 2001
in connection with the registration under the Securities Act of 1933, as
amended, of 3,000,000 additional shares of the Common Stock, $.01 par value per
share, including related plan interests (the "Common Stock"), of the Company to
be offered and sold pursuant to the Ameren Corporation Savings Investment Plan.

         As Vice President, General Counsel and Secretary of the Company, I have
examined the Restated Articles of Incorporation and the By-laws of the Company,
each as amended to the date hereof, the records of corporate proceedings and
other actions taken by the Company in connection with the authorization,
issuance and sale of the Common Stock and such other documents and materials as
I have deemed necessary or appropriate to enable me to deliver this opinion.

         Based on the foregoing, I am of the opinion that:

         Subject to (a) compliance with applicable state securities laws and (b)
the filing and effectiveness of the Registration Statement with the Securities
and Exchange Commission, the Common Stock, when issued and sold in the manner
described in the Registration Statement, will be legally issued, fully paid and
nonassessable.

         I hereby consent to the filing of this opinion as an exhibit to the
Registration Statement.


                                                   Yours truly,


                                                   /s/ Steven R. Sullivan
                                                  -------------------------
                                                       Steven R. Sullivan
                                                       Vice President,
                                                       General Counsel
                                                       and Secretary
                                                       Ameren Corporation


                                      II-6





                                                                   EXHIBIT 23.1



                       CONSENT OF INDEPENDENT ACCOUNTANTS


         We hereby consent to the incorporation by reference in this
Registration Statement on Form S-8 of our report dated February 5, 2001 relating
to the financial statements, which appears in the 2000 Annual Report to
Shareholders of Ameren Corporation, which is incorporated by reference in Ameren
Corporation's Annual Report on Form 10-K for the year ended December 31, 2000.
We also consent to the incorporation by reference of our report dated February
5, 2001 relating to the financial statement schedule, which appears in such
Annual Report on Form 10-K.

         We also consent to the incorporation by reference in this Registration
Statement of our report dated June 28, 2001 relating to the financial
statements, which appears in the Annual Report on Form 11-K of the Ameren
Corporation Savings Investment Plan for the year ended December 31, 2000.



/s/ PricewaterhouseCoopers LLP
--------------------------------
PricewaterhouseCoopers LLP
St. Louis, Missouri
October 24, 2001


                                      II-7









                                                                     EXHIBIT 24
                                POWER OF ATTORNEY

          WHEREAS, AMEREN CORPORATION, a Missouri corporation (herein referred
to as the "Company"), is required to file with the Securities and Exchange
Commission, under the Securities Act of 1933, a Registration Statement and any
amendments thereto, covering the registration of Common Stock under the Ameren
Corporation Savings Investment Plan, as authorized by the Company's Board of
Directors on October 12, 2001; and

          WHEREAS, each of the below undersigned holds the office or offices in
the Company set opposite his or her name;

          NOW THEREFORE, each of the undersigned hereby constitutes and appoints
Charles W. Mueller and/or Gary L. Rainwater and/or Warner L. Baxter and/or
Steven R. Sullivan the true and lawful attorneys-in-fact of the undersigned, for
and in the name, place and stead of the undersigned, to affix the name of the
undersigned to said Registration Statement and any amendments thereto, and, for
the performance of the same acts, each with power to appoint in their place and
stead and as their substitute, one or more attorneys-in-fact for the
undersigned, with full power of revocation; hereby ratifying and confirming all
that said attorneys-in-fact may do by virtue hereof.

          IN WITNESS WHEREOF, the undersigned have hereunto set their hands on
this 22nd day of October, 2001:

          Charles W. Mueller, Chairman,
                  Chief Executive Officer and Director
                  (Principal Executive Officer)        /s/ CHARLES W. MUELLER
                                                       -------------------------
          Warner L. Baxter, Senior Vice President, Finance
                  (Principal Financial Officer)        /s/ WARNER L. BAXTER
                                                       -------------------------
          Martin J. Lyons, Controller
                  (Principal Accounting Officer)       /s/ Martin J. Lyons
                                                       -------------------------
          William E. Cornelius, Director               /s/ WILLIAM E. CORNELIUS
                                                       -------------------------
          Clifford L. Greenwalt, Director              /s/ CLIFFORD L. GREENWALT
                                                       -------------------------
          Thomas A. Hays, Director
                                                       -------------------------
          Thomas H. Jacobsen, Director
                                                       -------------------------
          Richard A. Liddy, Director                   /S/ RICHARD A. LIDDY
                                                       -------------------------
          Gordon R. Lohman, Director
                                                       -------------------------
          Richard A. Lumpkin, Director
                                                       -------------------------
          John Peters MacCarthy, Director              /S/ JOHN PETERS MACCARTHY
                                                       -------------------------
          Hanne M. Merriman, Director                  /S/ HANNE M. MERRIMAN
                                                       -------------------------
          Paul L. Miller, Jr., Director                /s/ PAUL L. MILLER, JR.
                                                       -------------------------
          Harvey Saligman, Director                    /S/ HARVEY SALIGMAN
                                                       -------------------------
          Janet McAfee Weakley, Director
                                                       -------------------------
          James W. Wogsland, Director                  /S/ JAMES W. WOGSLAND
                                                       -------------------------

STATE OF MISSOURI  )
                   )   SS.
CITY OF ST. LOUIS  )

          On this 22nd day of October, 2001, before me, the undersigned Notary
Public in and for said State, personally appeared the above-named officers and
directors of Ameren Corporation, known to me to be the persons described in and
who executed the foregoing power of attorney and acknowledged to me that they
executed the same as their free act and deed for the purposes therein stated.

          IN TESTIMONY WHEREOF, I have hereunto set my hand and affixed my
official seal.
                                                  /s/ K.A Bell
                                                  -----------------------------
                                                  Notary Public - Notary Seal
                                                  STATE OF MISSOURI
                                                  City of St. Louis

                                      II-8



                                              October 24, 2001



           Securities and Exchange Commission
           Judiciary Plaza
           450 Fifth Street, N.W.
           Washington, D.C.  20549

           ATTN:  Document Control - EDGAR

                    Re:    Ameren Corporation - Registration  Statement on Form
                           S-8 Relating to 3,000,000 Additional Shares of
                           Common Stock, Including Related Plan Interests

           Ladies and Gentlemen:

                    We enclose for filing the Registration Statement on Form S-8
           of Ameren Corporation for the registration of the above-captioned
           securities.

                    If you have any questions or comments concerning this
           filing, please contact Ronald K. Evans, Assistant Secretary, at (314)
           554-2156 or revans@ameren.com

                                             Very truly yours,

                                             AMEREN CORPORATION


                                             By  /s/ Steven R. Sullivan
                                               --------------------------
                                                     STEVEN R. SULLIVAN
                                                     Secretary