PAGE  1
000 A000000 04/30/2007
000 C000000 0000878242
000 D000000 N
000 E000000 NF
000 F000000 Y
000 G000000 N
000 H000000 N
000 I000000 6.1
000 J000000 A
001 A000000 NUVEEN INSURED MUNI OPPORTUNITY FUND, INC.
001 B000000 811-06379
001 C000000 3129178200
002 A000000 333 WEST WACKER DRIVE
002 B000000 CHICAGO
002 C000000 IL
002 D010000 60606
002 D020000 1286
003  000000 N
004  000000 N
005  000000 N
006  000000 N
007 A000000 N
007 B000000  0
007 C010100  1
007 C010200  2
007 C010300  3
007 C010400  4
007 C010500  5
007 C010600  6
007 C010700  7
007 C010800  8
007 C010900  9
007 C011000 10
008 A000001 NUVEEN ASSET MANAGEMENT
008 B000001 A
008 C000001 801-14147
008 D010001 CHICAGO
008 D020001 IL
008 D030001 60606
008 D040001 1286
012 A000001 EQUISERVE INC.
012 B000001 84-05925
012 C010001 PROVIDENCE
012 C020001 RI
012 C030001 02940
013 A000001 ERNST & YOUNG LLP
013 B010001 CHICAGO
013 B020001 IL
013 B030001 60606
014 A000001 NUVEEN INVESTMENTS, LLC
014 B000001 8-13464
      PAGE  2
015 A000001 STATE STREET BANK AND TRUST COMPANY
015 B000001 C
015 C010001 BOSTON
015 C020001 MA
015 C030001 02110
015 E010001 X
018  000000 Y
019 A000000 Y
019 B000000  175
019 C000000 NUVEENFUND
020 C000001      0
020 C000002      0
020 C000003      0
020 C000004      0
020 C000005      0
020 C000006      0
020 C000007      0
020 C000008      0
020 C000009      0
020 C000010      0
021  000000        0
022 A000001 CITIGROUP
022 B000001 13-3214963
022 C000001     36551
022 D000001     33761
022 A000002 JPMORGAN CHASE
022 B000002 13-3224016
022 C000002     31269
022 D000002     38318
022 A000003 GOLDMAN SACHS
022 B000003 13-5108880
022 C000003     19579
022 D000003      5148
022 A000004 MORGAN STANLEY
022 B000004 13-2655998
022 C000004      5893
022 D000004     11807
022 A000005 LEHMAN BROTHERS, INC
022 B000005 13-2518466
022 C000005     11761
022 D000005         0
022 A000006 UBS
022 B000006 13-2638166
022 C000006         0
022 D000006     11706
022 A000007 RAYMOND JAMES
022 B000007 59-1237041
022 C000007      7169
022 D000007         0
022 A000008 BOSC INC
022 B000008 73-1275307
      PAGE  3
022 C000008         0
022 D000008      2662
022 A000009 BEAR STEARNS
022 B000009 13-3604093
022 C000009      2008
022 D000009         0
022 A000010 CABRERA CAPITAL MARKETS
022 B000010 39-1384463
022 C000010      1301
022 D000010         0
023 C000000     115531
023 D000000     104522
024  000000 N
025 D000001       0
025 D000002       0
025 D000003       0
025 D000004       0
025 D000005       0
025 D000006       0
025 D000007       0
025 D000008       0
026 A000000 N
026 B000000 N
026 C000000 N
026 D000000 Y
026 E000000 N
026 F000000 N
026 G010000 N
026 G020000 N
026 H000000 N
027  000000 N
028 A010000         0
028 A020000         0
028 A030000         0
028 A040000         0
028 B010000         0
028 B020000         0
028 B030000         0
028 B040000         0
028 C010000         0
028 C020000         0
028 C030000         0
028 C040000         0
028 D010000         0
028 D020000         0
028 D030000         0
028 D040000         0
028 E010000         0
028 E020000         0
028 E030000         0
028 E040000         0
      PAGE  4
028 F010000         0
028 F020000         0
028 F030000         0
028 F040000         0
028 G010000         0
028 G020000         0
028 G030000         0
028 G040000         0
028 H000000         0
030 A000000      0
030 B000000  0.00
030 C000000  0.00
031 A000000      0
031 B000000      0
032  000000      0
033  000000      0
035  000000      0
036 B000000      0
038  000000      0
042 A000000   0
042 B000000   0
042 C000000   0
042 D000000   0
042 E000000   0
042 F000000   0
042 G000000   0
042 H000000   0
043  000000      0
044  000000      0
045  000000 Y
046  000000 N
047  000000 N
048  000000  0.000
048 A010000        0
048 A020000 0.000
048 B010000        0
048 B020000 0.000
048 C010000        0
048 C020000 0.000
048 D010000        0
048 D020000 0.000
048 E010000        0
048 E020000 0.000
048 F010000        0
048 F020000 0.000
048 G010000        0
048 G020000 0.000
048 H010000        0
048 H020000 0.000
048 I010000        0
048 I020000 0.000
      PAGE  5
048 J010000        0
048 J020000 0.000
048 K010000        0
048 K020000 0.000
049  000000 N
050  000000 N
051  000000 N
052  000000 Y
053 A000000 N
054 A000000 Y
054 B000000 N
054 C000000 N
054 D000000 N
054 E000000 N
054 F000000 N
054 G000000 N
054 H000000 Y
054 I000000 N
054 J000000 Y
054 K000000 N
054 L000000 N
054 M000000 Y
054 N000000 N
054 O000000 Y
055 A000000 N
055 B000000 N
056  000000 Y
057  000000 N
058 A000000 N
059  000000 Y
060 A000000 Y
060 B000000 Y
061  000000        0
062 A000000 Y
062 B000000   0.0
062 C000000   0.0
062 D000000   0.0
062 E000000   0.0
062 F000000   0.0
062 G000000   0.0
062 H000000   0.0
062 I000000   0.0
062 J000000   0.0
062 K000000   0.0
062 L000000   0.0
062 M000000   0.0
062 N000000   0.0
062 O000000 157.6
062 P000000   0.0
062 Q000000   0.0
062 R000000   0.0
      PAGE  6
063 A000000   0
063 B000000  6.5
064 A000000 Y
064 B000000 N
066 A000000 N
067  000000 N
068 A000000 N
068 B000000 N
069  000000 N
070 A010000 Y
070 A020000 N
070 B010000 N
070 B020000 N
070 C010000 Y
070 C020000 N
070 D010000 N
070 D020000 N
070 E010000 Y
070 E020000 N
070 F010000 N
070 F020000 N
070 G010000 Y
070 G020000 N
070 H010000 N
070 H020000 N
070 I010000 N
070 I020000 N
070 J010000 Y
070 J020000 N
070 K010000 N
070 K020000 N
070 L010000 N
070 L020000 N
070 M010000 N
070 M020000 N
070 N010000 N
070 N020000 N
070 O010000 Y
070 O020000 Y
070 P010000 N
070 P020000 N
070 Q010000 N
070 Q020000 N
070 R010000 N
070 R020000 N
071 A000000     91579
071 B000000     61135
071 C000000   1974531
071 D000000    3
072 A000000  6
072 B000000    48019
      PAGE  7
072 C000000        0
072 D000000        0
072 E000000        0
072 F000000     5722
072 G000000        0
072 H000000        0
072 I000000       99
072 J000000       55
072 K000000       32
072 L000000       63
072 M000000       18
072 N000000        0
072 O000000        0
072 P000000     1386
072 Q000000        0
072 R000000       28
072 S000000       12
072 T000000        0
072 U000000        0
072 V000000        0
072 W000000     1029
072 X000000     8444
072 Y000000        0
072 Z000000    39575
072AA000000      599
072BB000000        0
072CC010000        0
072CC020000    12296
072DD010000    29940
072DD020000        0
072EE000000     1542
073 A010000   0.3690
073 A020000   0.0000
073 B000000   0.0190
073 C000000   0.0000
074 A000000        0
074 B000000        0
074 C000000        0
074 D000000  1966338
074 E000000        0
074 F000000        0
074 G000000        0
074 H000000        0
074 I000000        0
074 J000000    29524
074 K000000        0
074 L000000    29494
074 M000000      197
074 N000000  2025553
074 O000000        0
074 P000000      941
      PAGE  8
074 Q000000        0
074 R010000        0
074 R020000        0
074 R030000        0
074 R040000    96982
074 S000000   680000
074 T000000  1247630
074 U010000    81138
074 U020000        0
074 V010000    15.38
074 V020000     0.00
074 W000000   0.0000
074 X000000     4667
074 Y000000    94767
075 A000000        0
075 B000000  1255324
076  000000    14.90
077 A000000 N
078  000000 N
080 C000000        0
081 B000000   0
082 B000000        0
083 B000000        0
084 B000000        0
086 A010000      0
086 A020000      0
086 B010000      0
086 B020000      0
086 C010000      0
086 C020000      0
086 D010000      0
086 D020000      0
086 E010000      0
086 E020000      0
086 F010000      0
086 F020000      0
087 A010000 COMMON STOCK
087 A020000 670984103
087 A030000 NIO
088 A000000 N
088 B000000 N
088 C000000 N
088 D000000 Y
SIGNATURE   STEPHEN D. FOY
TITLE       V.P. & CONTROLLER