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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2007-03-01</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001279715</issuerCik>
        <issuerName>NATIONAL PATENT DEVELOPMENT CORP</issuerName>
        <issuerTradingSymbol>NPDV</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001222708</rptOwnerCik>
            <rptOwnerName>BELKNAP JOHN C</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>NATIONAL PATENT DEVELOPMENT CORPORATION</rptOwnerStreet1>
            <rptOwnerStreet2>777 WESTCHESTER AVENUE</rptOwnerStreet2>
            <rptOwnerCity>WHITE PLAINS</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10604</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Option to purchase common stock</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>2.45</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2007-03-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>218760</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2007-12-01</value>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <value>2017-03-01</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>218760</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>218760</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Options to purchase an aggregate of 400,000 shares of common stock were granted to Mr. Belknap under the 2003 Incentive Stock Plan (the &quot;Plan&quot;) on March 1, 2007, of which the grant of options to purchase 181,240 shares are subject to approval by the shareholders of the issuer of an amendment to the Plan.  Because the option to purchase 181,240 shares were granted subject to shareholder approval of the amendment to the Plan, such portion of the grant is not being reported on this Form 4.</footnote>
        <footnote id="F2">The options to purchase common stock will vest under the following schedule:  one-third of the option will vest on December 1, 2007, one-third of the options will vest on December 1, 2008 and the remaining one-third of the options will vest on December 1, 2009.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>John C. Belknap</signatureName>
        <signatureDate>2007-03-06</signatureDate>
    </ownerSignature>
</ownershipDocument>
