Ownership Submission
FORM 4
Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).
UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940
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(Print or Type Responses)
1. Name and Address of Reporting Person *
CITIGROUP INC
   2. Issuer Name and Ticker or Trading Symbol
NUVEEN INSURED MUNICIPAL OPPORTUNITY FUND INC [NIO] 		5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)
_____ Director __X__ 10% Owner
_____ Officer (give title below) _____ Other (specify below)
(Last)
(First)
(Middle)
399 PARK AVENUE		 3. Date of Earliest Transaction (Month/Day/Year)
01/24/2011
(Street)

NEW YORK, NY 10043		 4. If Amendment, Date Original Filed(Month/Day/Year)
 6. Individual or Joint/Group Filing(Check Applicable Line)
_X_ Form filed by One Reporting Person
___ Form filed by More than One Reporting Person
(City)
(State)
(Zip)
Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1.Title of Security
(Instr. 3)		 2. Transaction Date (Month/Day/Year) 2A. Deemed Execution Date, if any (Month/Day/Year) 3. Transaction Code
(Instr. 8)		 4. Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4 and 5)		 5. Amount of Securities Beneficially Owned Following Reported Transaction(s)
(Instr. 3 and 4)		 6. Ownership Form: Direct (D) or Indirect (I)
(Instr. 4)		 7. Nature of Indirect Beneficial Ownership
(Instr. 4)
Code V Amount (A) or (D) Price
Auction Rate Preferred 01/24/2011   J(1)   316 D $ 25,001.25 1,202 I By Subsidiary (2)
Auction Rate Preferred 01/25/2011   J(1)   742 D $ 25,001.41 460 I By Subsidiary (2)
Auction Rate Preferred 01/26/2011   J(1)   460 D $ 25,001.41 0 I By Subsidiary (2)

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
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Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security
(Instr. 3)		 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (Month/Day/Year) 3A. Deemed Execution Date, if any (Month/Day/Year) 4. Transaction Code
(Instr. 8)		 5. Number of Derivative Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4, and 5)		 6. Date Exercisable and Expiration Date
(Month/Day/Year)		 7. Title and Amount of Underlying Securities
(Instr. 3 and 4)		 8. Price of Derivative Security
(Instr. 5)		 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s)
(Instr. 4)		 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I)
(Instr. 4)		 11. Nature of Indirect Beneficial Ownership
(Instr. 4)
Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares

Reporting Owners

Reporting Owner Name / Address Relationships
 Director  10% Owner  Officer  Other
CITIGROUP INC
399 PARK AVENUE
NEW YORK, NY 10043		     X    

Signatures

 Citigroup Inc., By: /s/ Ali L. Karshan, Assistant Secretary   01/26/2011
**Signature of Reporting Person Date

Explanation of Responses:

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
(1) These Auction Preferred Shares ("Shares") were called for redemption by the issuer.
(2) The Shares reported in Table I represent Shares beneficially owned by Citigroup Global Markets Inc. ("CGMI"). Citigroup Financial Products Inc. ("CFP") is the sole stockholder of CGMI. Citigroup Global Markets Holdings Inc. ("CGMH") is the sole stockholder of CFP. Citigroup Inc. is the sole stockholder of CGMH.
 
Remarks:
The Shares reported herein represent the Reporting Person's combined holdings in multiple series of auction preferred securities of the issuer which are treated herein as one class of securities consistent with the Reporting Person's prior Section 16 filings made in respect of the issuer.

Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.

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