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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2014-08-05</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000916907</issuerCik>
        <issuerName>SOUTHERN MISSOURI BANCORP INC</issuerName>
        <issuerTradingSymbol>SMBC</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001615302</rptOwnerCik>
            <rptOwnerName>Hensley Todd E.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>SOUTHERN MISSOURI BANCORP, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>531 VINE STREET</rptOwnerStreet2>
            <rptOwnerCity>POPLAR BLUFF</rptOwnerCity>
            <rptOwnerState>MO</rptOwnerState>
            <rptOwnerZipCode>63901</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2014-08-05</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>266020</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>266020</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Received in exchange for shares of the common stock of Peoples Service Company (&quot;PSC&quot;) in connection with the merger of PSC with and into Southern Missouri Bancorp, Inc. (&quot;SMBI&quot;). Under the terms of the merger agreement between SMBI and PSC, at the effective time of the merger, each share of PSC common stock outstanding immediately prior to the effective time was exchanged for $11.50  in cash plus .3289 of a share of SMBI common stock.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Todd E. Hensley, Director</signatureName>
        <signatureDate>2014-08-05</signatureDate>
    </ownerSignature>
</ownershipDocument>
