<?xml version="1.0"?>

<ownershipDocument>

    <documentType>4</documentType>

    <periodOfReport>2003-06-25</periodOfReport>


    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000737875</issuerCik>
        <issuerName>FIRST KEYSTONE CORP</issuerName>
        <issuerTradingSymbol>FKYS</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001236272</rptOwnerCik>
            <rptOwnerName>BAZEWICZ J GERALD</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>  </rptOwnerStreet1>
            <rptOwnerStreet2>  </rptOwnerStreet2>
            <rptOwnerCity>  </rptOwnerCity>
            <rptOwnerState>  </rptOwnerState>
            <rptOwnerZipCode>  </rptOwnerZipCode>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>CEO/President</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeSecurity>
        <securityTitle>
            <value>First Keystone Corporation</value>
        </securityTitle>
        <transactionDate>
            <value>2003-06-25</value>
        </transactionDate>
        <deemedExecutionDate>
            <value>2003-06-25</value>
        </deemedExecutionDate>
        <transactionCoding>
            <transactionFormType>4</transactionFormType>
            <transactionCode>M</transactionCode>
            <equitySwapInvolved>0</equitySwapInvolved>
        </transactionCoding>
        <transactionTimeliness>
            <value></value>
        </transactionTimeliness>
        <transactionAmounts>
            <transactionShares>
                <value>2100</value>
            </transactionShares>
            <transactionValue>
                <value>16.19</value>
            </transactionValue>
            <transactionAcquiredDisposedCode>
                <value>A</value>
            </transactionAcquiredDisposedCode>
        </transactionAmounts>
        <postTransactionAmounts>
            <sharesOwnedFollowingTransaction>
                <value>17855.9573</value>
            </sharesOwnedFollowingTransaction>
        </postTransactionAmounts>
        <ownershipNature>
            <directOrIndirectOwnership>
                <value>D</value>
            </directOrIndirectOwnership>
        </ownershipNature>
    </nonDerivativeSecurity>

    <derivativeSecurity>
        <securityTitle>
            <value>Employee Stock Option (right to buy)</value>
        </securityTitle>
        <conversionOrExercisePrice>
            <value>16.19</value>
        </conversionOrExercisePrice>
        <transactionDate>
            <value>2003-06-25</value>
        </transactionDate>
        <transactionCoding>
            <transactionFormType>4</transactionFormType>
            <transactionCode>M</transactionCode>
            <equitySwapInvolved>0</equitySwapInvolved>
        </transactionCoding>
        <transactionTimeliness>
            <value></value>
        </transactionTimeliness>
        <transactionAmounts>
            <transactionShares>
                <value>2100</value>
            </transactionShares>
            <transactionValue>
                <value>16.19</value>
            </transactionValue>
            <transactionAcquiredDisposedCode>
                <value>D</value>
            </transactionAcquiredDisposedCode>
        </transactionAmounts>
        <exerciseDate>
            <value>2001-03-26</value>
        </exerciseDate>
        <expirationDate>
            <value>2010-09-26</value>
        </expirationDate>
        <underlyingSecurity>
            <underlyingSecurityTitle>
                <value>Common Stock</value>
            </underlyingSecurityTitle>
            <underlyingSecurityShares>
                <value>2100</value>
            </underlyingSecurityShares>
        </underlyingSecurity>
        <postTransactionAmounts>
            <sharesOwnedFollowingTransaction>
                <value>0</value>
            </sharesOwnedFollowingTransaction>
        </postTransactionAmounts>
        <ownershipNature>
            <directOrIndirectOwnership>
                <value>D</value>
            </directOrIndirectOwnership>
        </ownershipNature>
    </derivativeSecurity>


    <ownerSignature>
        <signatureName>/s/ J. Gerald Bazewicz</signatureName>
        <signatureDate>2003-06-25</signatureDate>
    </ownerSignature>

</ownershipDocument>
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4
2003-06-25
0
0000737875
FIRST KEYSTONE CORP
FKYS
0001236272
BAZEWICZ J GERALD
1
1
0
0
CEO/President
First Keystone Corporation
2003-06-25
2003-06-25
4
M
0
2100
16.19
A
17855.9573
D
Employee Stock Option (right to buy)
16.19
2003-06-25
4
M
0
2100
16.19
D
2001-03-26
2010-09-26
Common Stock
2100
0
D
/s/ J. Gerald Bazewicz
2003-06-25