<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2008-12-18</periodOfReport>

    <notSubjectToSection16>1</notSubjectToSection16>

    <issuer>
        <issuerCik>0001068875</issuerCik>
        <issuerName>INFOSPACE INC</issuerName>
        <issuerTradingSymbol>INSP</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0000065100</rptOwnerCik>
            <rptOwnerName>MERRILL LYNCH &amp; CO INC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>4 WORLD FINANCIAL CTR</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10080</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0000728612</rptOwnerCik>
            <rptOwnerName>MERRILL LYNCH PIERCE FENNER &amp; SMITH INC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>4 WORLD FINANCIAL CENTER</rptOwnerStreet1>
            <rptOwnerStreet2>NORTH TOWER</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10080</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock, Par Value $.0001</value>
            </securityTitle>
            <transactionDate>
                <value>2008-12-18</value>
            </transactionDate>
            <deemedExecutionDate>
                <value>2008-12-18</value>
            </deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>393</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>7.82</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4943416</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnotes</value>
                    <footnoteId id="F1"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock, Par Value $.0001 per share</value>
            </securityTitle>
            <transactionDate>
                <value>2008-12-19</value>
            </transactionDate>
            <deemedExecutionDate>
                <value>2008-12-19</value>
            </deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>131</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>7.8</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4943547</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnotes</value>
                    <footnoteId id="F1"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock, Par Value $.0001 per share</value>
            </securityTitle>
            <transactionDate>
                <value>2008-12-19</value>
            </transactionDate>
            <deemedExecutionDate>
                <value>2008-12-19</value>
            </deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>131</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>7.8</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4973416</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnotes</value>
                    <footnoteId id="F1"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock, Par Value $.0001</value>
            </securityTitle>
            <transactionDate>
                <value>2008-12-22</value>
            </transactionDate>
            <deemedExecutionDate>
                <value>2008-12-22</value>
            </deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>2405810</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>7.38</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2537606</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnotes</value>
                    <footnoteId id="F1"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Merrill Lynch &amp; Co., Inc. indirectly through its wholly-owned subsidiary Merrill Lynch, Pierce, Fenner &amp; Smith Incorporated owned 2,537,606.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Pia K. Thompson</signatureName>
        <signatureDate>2008-12-23</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0303
4
2008-12-18
1
0001068875
INFOSPACE INC
INSP
0000065100
MERRILL LYNCH & CO INC
4 WORLD FINANCIAL CTR
NEW YORK
NY
10080
0
0
1
0
0000728612
MERRILL LYNCH PIERCE FENNER & SMITH INC
4 WORLD FINANCIAL CENTER
NORTH TOWER
NEW YORK
NY
10080
0
0
1
0
Common Stock, Par Value $.0001
2008-12-18
2008-12-18
4
P
0
393
7.82
A
4943416
I
See footnotes
Common Stock, Par Value $.0001 per share
2008-12-19
2008-12-19
4
P
0
131
7.8
A
4943547
I
See footnotes
Common Stock, Par Value $.0001 per share
2008-12-19
2008-12-19
4
S
0
131
7.8
D
4973416
I
See footnotes
Common Stock, Par Value $.0001
2008-12-22
2008-12-22
4
S
0
2405810
7.38
D
2537606
I
See footnotes
Merrill Lynch & Co., Inc. indirectly through its wholly-owned subsidiary Merrill Lynch, Pierce, Fenner & Smith Incorporated owned 2,537,606.
Pia K. Thompson
2008-12-23