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

FORM N-Q

QUARTERLY SCHEDULE OF PORTFOLIO HOLDINGS OF REGISTERED
MANAGEMENT INVESTMENT COMPANY

Investment Company Act file number:           811-21178               

                         BlackRock Insured Municipal Income Trust                         
(Exact name of registrant as specified in charter)

 

                    100 Bellevue Parkway, Wilmington, DE                                     19809                
(Address of principal executive offices) 
(Zip code) 

Robert S. Kapito, President
BlackRock Insured Municipal Income Trust
40 East 52nd Street, New York, NY 10022
(Name and address of agent for service)

Registrant's telephone number, including area code:           888-825-2257               

Date of fiscal year end:           August 31, 2006               

Date of reporting period:           May 31, 2006               


Item 1. Schedule of Investments.
The Registrant’s unaudited schedule of investments as of the close of the reporting period pursuant to Rule 30b1-5 under the Investment Company Act of 1940 is as follows:

PORTFOLIO OF INVESTMENTS (unaudited)
MAY 31, 2006

BlackRock Insured Municipal Income Trust (BYM)

    Principal            
    Amount       Option Call    
Rating1   (000)     Description   Provisions2   Value  

            LONG-TERM INVESTMENTS—152.3%        
        Alabama—1.8%        
        Birmingham Wtr. Wks. & Swr. Brd. RB,        
AAA   $ 1,140       Ser. A, 4.50%, 1/01/35, FSA   01/16 @ 100   $     1,099,108  
AAA   3,705       Ser. A, 5.00%, 1/01/40, FSA   01/16 @ 100   3,792,623  
AAA   2,180       Ser. A, 5.00%, 1/01/43, FSA   01/16 @ 100   2,228,178  

                7,119,909  

        California—36.5%        
        California St. GO,        
AAA   5,000       5.00%, 2/01/32, MBIA   08/13 @ 100   5,114,350  
AAA   5,000       5.00%, 3/01/33   03/15 @ 100   5,113,350  
A   14,000 3 Dept. of Wtr. Res., Pwr. Sply. RB, Ser. A, 5.375%, 5/01/12   N/A   15,346,100  
        Golden St. Tobacco Sec. Corp. RB,        
AAA   10,000       Ser. A, 5.00%, 6/01/35, FGIC   06/15 @ 100   10,220,000  
BBB   6,500       Ser. A-1, 6.625%, 6/01/40   06/13 @ 100   7,209,475  
BBB   14,500       Ser. A-1, 6.75%, 6/01/39   06/13 @ 100   16,189,395  
AAA   12,100 3 Infrastructure & Econ. Dev. RB, Bay Area Toll Brdgs. Proj., Ser. A, 5.00%, 1/01/28, AMBAC   N/A   12,981,485  
AAA   17,500   Met. Wtr. Dist. So. California RB, Ser. B-1, 5.00%, 10/01/33, FGIC   10/13 @ 100   17,984,575  
AAA   15,000   San Francisco City & Cnty. Pub. Utils. Comm. Wtr. RB, Ser. A, 5.00%, 11/01/31, FSA   11/11 @ 100   15,420,900  
AAA   53,000   San Joaquin Hills Transp. Corridor Agcy. Toll Rd. RB, Ser. A, Zero Coupon, 1/15/31, MBIA   No Opt. Call   15,568,750  
        Univ. of California RB,        
AAA   10,000       Ser. C, 4.75%, 5/15/37, MBIA   05/13 @ 101   9,919,600  
AAA   3,330       Ser. G, 4.75%, 5/15/31, MBIA   05/13 @ 101   3,325,071  
AAA   10,910       Ser. O, 5.00%, 9/01/28, FGIC   09/10 @ 101   11,271,994  

                145,665,045  

        District of Columbia—2.6%        
BBB   9,500   Tobacco Settlement Financing Corp. RB, 6.75%, 5/15/40   05/11 @ 101   10,239,290  

        Florida—3.0%        
AAA   1,880   JEA Wtr. & Swr. Sys. RB, Ser. A, 4.75%, 10/01/36, MBIA   04/11 @ 100   1,856,068  
AAA   25,520   Miami Dade Cnty. RB, Cap. Apprec. Proj., Ser. A, Zero Coupon, 10/01/38, MBIA   10/15 @ 30.363   4,734,981  
AAA   5,485   Orange Cnty. Tourist Dev. Tax RB, 4.75%, 10/01/32   10/16 @ 100   5,476,443  

                12,067,492  

        Georgia—4.4%        
AAA   2,500   Atlanta Arpt. Passenger Fac. RB, Ser. J, 5.00%, 1/01/34, FSA   01/15 @ 100   2,562,975  
        Atlanta Wtr. & Wstwtr. RB,    
AAA   2,000       5.00%, 11/01/34, FSA   11/14 @ 100   2,050,960  
AAA   3,235       5.00%, 11/01/37, FSA   11/14 @ 100   3,308,370  
AAA   9,555       Ser. A, 5.00%, 11/01/38, FGIC   05/09 @ 101   9,804,099  

                17,726,404  

        Illinois—16.3%        
        Chicago GO,        
AAA   13,000       Ser. A, 5.00%, 1/01/34, FSA   01/14 @ 100   13,278,850  
AAA   7,000       Ser. A, 5.00%, 1/01/34, MBIA   01/13 @ 100   7,149,030  
AAA   11,550 3 Chicago Spec. Transp. RB, 5.25%, 1/01/27, AMBAC   01/11 @ 101   12,135,354  
        Met. Pier & Exposition Auth. Ded. St. Tax RB, McCormick Place Expansion Proj.,        
AAA   24,010       Ser. A, 5.00%, 12/15/28, MBIA   06/12 @ 101   24,682,520  
AAA   15,000       Ser. B, Zero Coupon, 6/15/28, MBIA   No Opt. Call   5,242,200  
AAA   2,400 4 O’Hare Intl. Arpt. RB, Ser. A, 5.00%, 1/01/30, MBIA   01/15 @ 100   2,455,344  

                64,943,298  

        Indiana—1.1%        
AAA   4,725   Mun. Pwr. Sply. Sys. RB, Ser. A, 4.50%, 1/01/32, AMBAC   01/16 @ 100   4,510,627  

        Louisiana—3.4%        
AAA   13,250   St. Gas & Fuels Tax RB, Ser. A, 5.00%, 5/01/35, FGIC   05/15 @ 100   13,555,280  

        Massachusetts—7.6%        
AA   5,985   St. Wtr. Res. Auth. Gen. RB, Ser. A, 5.00%, 8/01/41   08/16 @ 100   6,133,188  
AAA   24,000   Tpke. Auth. Met. Hwy. Sys. RB, Ser. A, 5.00%, 1/01/39, AMBAC   01/09 @ 101   24,359,520  

                30,492,708  

        Minnesota—1.3%        
AAA   5,000   St. Paul Met. Arpt. Comm. RB, 5.00%, 1/01/35, AMBAC   01/15 @ 100   5,118,850  

1


BlackRock Insured Municipal Income Trust (BYM)

  Principal            
    Amount       Option Call    
Rating1    (000)     Description   Provisions2   Value  

            Missouri—1.3%        
AAA   $ 5,500   Joint Mun. Elec. Util. Comm. RB, Plum Point Proj., 4.60%, 1/01/36, MBIA   01/16 @ 100   $     5,386,590  

        Nebraska—1.0%        
AA   4,280   Omaha Pub. Pwr. Dist. Elec. Sys. RB, Ser. A, 4.75%, 2/01/44   02/14 @ 100   4,177,066  

        Nevada—7.2%        
AAA   6,000 3 Reno RB, Transp. Proj., 5.125%, 6/01/12, AMBAC   N/A   6,412,320  
        Truckee Meadows Wtr. Auth. RB,        
AAA   10,000       Ser. A, 5.00%, 7/01/25, FSA   07/11 @ 100   10,228,700  
AAA   6,500       Ser. A, 5.125%, 7/01/30, FSA   07/11 @ 100   6,702,995  
AAA   5,000 3     Ser. A, 5.25%, 7/01/11, FSA   N/A   5,343,350  

                28,687,365  

        New York—8.0%        
AAA   2,980   Convention Ctr. Dev. RB, Hotel Unit Fee Secured, 5.00%, 11/15/44, AMBAC   11/15 @ 100   3,056,616  
        New York City Mun. Wtr. Fin. Auth. Wtr. & Swr. Sys. RB,        
AAA   10,650       Ser. B, 5.00%, 6/15/36, FSA   12/14 @ 100   10,977,914  
AAA   7,305       Ser. C, 5.00%, 6/15/35, AMBAC   06/14 @ 100   7,518,963  
AAA   10,000   New York City Trust Cultural Recs. RB, American Museum of Natural History Proj., Ser. A,        
            5.00%, 7/01/44, MBIA   07/14 @ 100   10,239,700  

                31,793,193  

        Ohio—4.5%        
AAA   12,280   Air Qual. Dev. Auth. RB, 4.80%, 1/01/34, FGIC   07/15 @ 100   12,223,758  
AAA   6,000   Wtr. Dev. Auth. Facs. PCRB, Dayton Pwr. & Lt. Proj., Ser. A, 4.80%, 1/01/34, FGIC   07/15 @ 100   5,927,460  

                18,151,218  

        Pennsylvania—2.7%        
BBB   5,000   Lebanon Cnty. Hlth. Facs. Auth. RB, Good Samaritan Hosp. Proj., 6.00%, 11/15/35   11/12 @ 101   5,310,650  
AAA   5,200 3 Philadelphia Gas Wks. RB, Ser. 3, 5.125%, 8/01/11, FSA   N/A   5,527,080  

                10,837,730  

        South Carolina—7.9%        
AAA   5,000   Pub. Svc. Auth. RB, Ser. B, 5.50%, 1/01/36, FSA   01/12 @ 100   5,307,050  
        Transp. Infrastructure Bank RB,        
AAA   12,750       Ser. A, 5.00%, 10/01/33, AMBAC   10/12 @ 100   13,033,177  
AAA   12,660       Ser. B, 5.125%, 10/01/26, AMBAC   10/11 @ 100   13,181,972  

                31,522,199  

        Tennessee—4.0%        
        Knox Cnty. Hlth. Edl. & Hsg. Facs. Brd. Hosp. Facs. RB,        
AAA   11,705       Ser. A, Zero Coupon, 1/01/22, FSA   01/13 @ 59.566   4,962,920  
AAA   9,260       Ser. A, Zero Coupon, 1/01/23, FSA   01/13 @ 56.016   3,685,202  
AAA   8,500       Ser. A, Zero Coupon, 1/01/24, FSA   01/13 @ 52.749   3,179,340  
AAA   6,850       Ser. A, Zero Coupon, 1/01/25, FSA   01/13 @ 49.712   2,414,625  
AAA   5,000       Ser. A, Zero Coupon, 1/01/26, FSA   01/13 @ 46.781   1,655,400  

                15,897,487  

        Texas—26.9%        
AAA   10,030   Coppell Indpt. Sch. Dist. GO, Zero Coupon, 8/15/30   No Opt. Call   3,029,461  
AAA   2,350   Dallas Area Rapid Trans. RB, 5.00%, 12/01/31, AMBAC   12/11 @ 100   2,392,841  
        Harris Cnty. Sports Auth. RB,        
AAA   26,890       Ser. A-3, Zero Coupon, 11/15/38, MBIA   11/24 @ 43.826   4,539,301  
AAA   27,675       Ser. A-3, Zero Coupon, 11/15/39, MBIA   11/24 @ 41.258   4,390,362  
AAA   5,785       Ser. H, Zero Coupon, 11/15/38, MBIA   11/31 @ 64.91   1,006,995  
AAA   6,160       Ser. H, Zero Coupon, 11/15/39, MBIA   11/31 @ 60.976   1,004,819  
        Harris Cnty.,        
AAA   7,485       GO, Zero Coupon, 8/15/25, MBIA   No Opt. Call   2,961,141  
AAA   10,915       GO, Zero Coupon, 8/15/28, MBIA   No Opt. Call   3,671,369  
AAA   5,510       RB, Toll Rd. Proj., 5.00%, 8/15/30, FSA   08/12 @ 100   5,633,204  
AAA   6,000   Lower Colorado Riv. Auth. RB, 4.75%, 5/15/36, AMBAC   05/11 @ 100   5,924,280  
AAA   1,045   Montgomery Cnty. Mun. Util. Dist. No. 46, Wtr. Wks. & Swr. Sys. GO, 4.75%, 3/01/30, MBIA   03/14 @ 100   1,037,570  
AAA   9,500   Northside Indpt. Sch. Dist. Sch. Bldg. GO, 5.125%, 6/15/29   06/14 @ 100   9,863,755  
AAA   3,000   Pearland GO, 4.75%, 3/01/29, FGIC   03/16 @ 100   2,987,400  
        San Antonio Wtr. RB,        
AAA   9,350       5.125%, 5/15/29, FGIC   05/14 @ 100   9,723,813  
AAA   10,000       5.125%, 5/15/34, FGIC   05/14 @ 100   10,352,500  
AAA   35,290   Tpke. Auth. Central Sys. RB, Ser. A, 5.00%, 8/15/42, AMBAC   08/12 @ 100   35,737,477  
BBB+   3,000   Tyler Cnty. Hlth. Facs. Dev. RB, Mother Frances Hosp. Proj., 6.00%, 7/01/31   07/12 @ 100   3,160,140  

                107,416,428  

2


BlackRock Insured Municipal Income Trust (BYM)

  Principal            
    Amount       Option Call    
Rating1       (000)     Description   Provisions2   Value  

        Virginia—1.9%        
        Chesterfield Cnty. Indl. Dev. Auth. PCRB, Elec. & Pwr. Co. Proj.,        
Baa1   $ 3,000       Ser. A, 5.875%, 6/01/17   11/10 @ 102   $     3,253,350  
Baa1   4,000       Ser. B, 5.875%, 6/01/17   11/10 @ 102   4,337,800  

                7,591,150  

        Washington—8.6%        
AAA   9,610   Central Washington Univ. Sys. RB, 5.00%, 5/01/34, FGIC   05/14 @ 100   9,836,315  
AAA   3,655   Chelan Cnty. Pub. Util. Dist. 1 RB, Chelan Hydro Sys. Proj., Ser. C, 5.125%, 7/01/33, AMBAC   07/12 @ 100   3,759,423  
AAA   4,500   Port of Seattle RB, Ser. A, 5.00%, 4/01/31, FGIC   10/11 @ 100   4,600,890  
AAA   9,500   Seattle GO, Ser. F, 5.125%, 12/15/28, MBIA   12/08 @ 100   9,717,740  
AAA   6,380   Washington GO, Ser. A, 5.00%, 7/01/25, FSA   07/11 @ 100   6,549,198  

                34,463,566  

        West Virginia—0.3%        
AAA   1,295   Econ. Dev. Auth. RB, Correctional Juvenile Safety Proj., Ser. A, 5.00%, 6/01/29, MBIA   06/14 @ 100   1,336,285  

        Total Long-Term Investments (cost $584,188,155)       608,699,180  

        SHORT-TERM INVESTMENTS—4.8%        
        Tennessee—0.1%        
VMIG1   500 5 Montgomery Cnty. Pub. Bldg. Auth. RB, 3.58%, 6/01/06, FRDD   N/A   500,000  

        Nebraska—3.7%        
A-1+   14,799 5 American Pub. Energy Agcy. Gas Sply. RB, Ser. A, 3.50%, 6/01/06, FRWD   N/A   14,799,000  

   
Shares
           
   
(000)
           

        Money Market Funds—1.0%        
NR   3,900   AIM Tax Free Investment Co. Cash Reserve Portfolio   N/A   3,900,000  

        Total Short-Term Investments (cost $19,199,000)       19,199,000  

        Total Investments—157.1% (cost $603,387,1556)       $ 627,898,180  
        Other assets in excess of liabilities—0.2%       710,346  
        Preferred shares at redemption value, including dividends payable—(57.3)%       (229,045,725)  

        Net Assets Applicable to Common Shareholders—100%       $ 399,562,801  


1   Using the higher of Standard & Poor’s, Moody’s Investors Service or Fitch’s rating.  
2   Date (month/year) and price of the earliest optional call or redemption. There may be other call provisions at varying prices at later dates.  
3   This bond is prerefunded. U.S. government securities, held in escrow, are used to pay interest on this security, as well as retire the bond in full at the date indicated, typically at a premium to par.  
4   Security pledged as collateral.  
5   For purposes of amortized cost valuation, the maturity date of this instrument is considered to be the earlier of the next date on which the security can be redeemed at par, or the next date on which the rate of interest is adjusted. Rate shown is rate as of May 31, 2006.  
6   Cost for Federal income tax purposes is $603,368,017. The net unrealized appreciation on a tax basis is $24,530,163, consisting of $25,307,678 gross unrealized appreciation and $777,515 gross unrealized depreciation.  
    The value (market value plus accrued interest) of securities that are covered by insurance, which ensures the payment of principal and interest, represent approximately 82.7% of the Trust’s managed assets. The Trust had the following insurance concentrations:  

AMBAC
24.2%
FGIC
19.0%
FSA
18.7%
MBIA
20.2%
Other
0.6%

KEY TO ABBREVIATIONS

AMBAC American Municipal Bond Assurance Corp. GO General Obligation
FGIC Financial Guaranty Insurance Co. MBIA Municipal Bond Insurance Assoc.
FRDD Floating Rate Daily Demand PCRB Pollution Control Revenue Bond
FRWD Floating Rate Weekly Demand RB Revenue Bond
FSA Financial Security Assurance    
 

3


Item 2. Controls and Procedures.
(a) The Registrant's principal executive and principal financial officers have evaluated the Registrant's disclosure controls and procedures within 90 days of this filing and have concluded, as of that date, that the Registrant’s disclosure controls and procedures were reasonably designed to ensure that information required to be disclosed by the Registrant in this Form N-Q was recorded, processed, summarized, and reported within the required time periods and that information to be disclosed by the Registrant in this Form N-Q was accumulated and communicated to the Registrant’s management, including its principal executive and principal financial officers, as appropriate, to allow timely decisions regarding required disclosure.

(b) There were no changes in the Registrant's internal control over financial reporting (as defined in Rule 30a-3(d) under the 1940 Act (17 CFR 270.30a-3(d)) that occurred during the Registrant's last fiscal quarter that have materially affected, or are reasonably likely to materially affect, the Registrant's internal control over financial reporting.

Item 3. Exhibits.
Separate certifications of the Registrant’s Principal Executive and Financial Officers pursuant to Section 302 of the Sarbanes-Oxley Act of 2002 are attached as EX-99.CERT.


SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940, the Registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

(Registrant)                BlackRock Insured Municipal Income Trust               

By:       /s/   Henry Gabbay                
Name: Henry Gabbay
Title: Treasurer and Principal Financial Officer
Date: July 26, 2006

     Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940, this report has been signed below by the following persons on behalf of the Registrant and in the capacities and on the dates indicated.

By:       /s/   Robert S. Kapito                
Name: Robert S. Kapito
Title: President and Principal Executive Officer
Date: July 26, 2006

By:       /s/   Henry Gabbay                
Name: Henry Gabbay
Title: Treasurer and Principal Financial Officer
Date: July 26, 2006