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

    <schemaVersion>X0303</schemaVersion>

    <documentType>4/A</documentType>

    <periodOfReport>2010-06-25</periodOfReport>

    <dateOfOriginalSubmission>2010-06-29</dateOfOriginalSubmission>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001030485</issuerCik>
        <issuerName>NEOMAGIC CORP</issuerName>
        <issuerTradingSymbol>nmgc</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001400660</rptOwnerCik>
            <rptOwnerName>Tomasello David</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>2372-A QUME DRIVE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>SAN JOSE</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>95131</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock option (right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>0.08</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2010-06-25</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>340000</value>
                    <footnoteId id="F3"/>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2012-06-25</value>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <value>2016-06-25</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>340000</value>
                    <footnoteId id="F3"/>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>18176667</value>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F2"/>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">The stock options were granted on June 23, 2010 and have an effective date of June 25, 2010, pursuant to the Company 2003 Stock Plan, as amended.  The shares subject to such option grant shall vest and become exercisable on each monthly anniversary of June 25, 2010 over a two year period, assuming continued service with the Company, on each scheduled vesting date.</footnote>
        <footnote id="F2">On October 12, 2009, NeoMagic Corporation entered into a Stock Purchase Agreement with investors, including Attiva Capital Management, LLC, and Bluestone Financial Ltd, of which Mr. Tomasello holds sole voting power, and 333,333 and 17,333,334 warrants are currently outstanding.  Mr. Tomasello disclaims beneficial ownership of the shares except to the extent of his pecuniary interest therein.</footnote>
        <footnote id="F3">This amendment is issue to correct the number of shares granted and to correct the total number of shares beneficially owned.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Charlotte Willson for David Tomasello</signatureName>
        <signatureDate>2010-06-29</signatureDate>
    </ownerSignature>
</ownershipDocument>
