<?xml version="1.0"?>

<ownershipDocument>

    <documentType>4</documentType>

    <periodOfReport>2003-05-29</periodOfReport>


    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000101382</issuerCik>
        <issuerName>UMB FINANCIAL CORP</issuerName>
        <issuerTradingSymbol>UMBF</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001209583</rptOwnerCik>
            <rptOwnerName>KEMPER R CROSBY JR</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>  </rptOwnerStreet1>
            <rptOwnerStreet2>  </rptOwnerStreet2>
            <rptOwnerCity>  </rptOwnerCity>
            <rptOwnerState>  </rptOwnerState>
            <rptOwnerZipCode>  </rptOwnerZipCode>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Sr. Chairman</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeSecurity>
        <securityTitle>
            <value>Common Stock</value>
        </securityTitle>
        <transactionDate>
            <value>2003-05-29</value>
        </transactionDate>
        <transactionCoding>
            <transactionFormType>4</transactionFormType>
            <transactionCode>S</transactionCode>
            <equitySwapInvolved>0</equitySwapInvolved>
        </transactionCoding>
        <transactionTimeliness>
            <value></value>
        </transactionTimeliness>
        <transactionAmounts>
            <transactionShares>
                <value>5000</value>
            </transactionShares>
            <transactionValue>
                <value>40</value>
            </transactionValue>
            <transactionAcquiredDisposedCode>
                <value>D</value>
            </transactionAcquiredDisposedCode>
        </transactionAmounts>
        <postTransactionAmounts>
            <sharesOwnedFollowingTransaction>
                <value>1823173</value>
                <footnoteId id="F1"/>
            </sharesOwnedFollowingTransaction>
        </postTransactionAmounts>
        <ownershipNature>
            <directOrIndirectOwnership>
                <value>D</value>
            </directOrIndirectOwnership>
        </ownershipNature>
    </nonDerivativeSecurity>

    <footnotes>
        <footnote id="F1">4,013.11 held indirectly by ESOP
154,645 held indirectly by Kemper Realty, Inc.
208,080 held indirectly by Pioneer Service Corporation
12,029 held indirectly by Spouse
92,150 held indirectly by Stagecoach Inc.
329,528 held indirectly by Stagecoach Investment, LP</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>John C. Pauls, by Power of Atty. for R. Crosby Kemper, Jr.</signatureName>
        <signatureDate>2003-05-27</signatureDate>
    </ownerSignature>

</ownershipDocument>
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4
2003-05-29
0
0000101382
UMB FINANCIAL CORP
UMBF
0001209583
KEMPER R CROSBY JR
1
1
1
0
Sr. Chairman
Common Stock
2003-05-29
4
S
0
5000
40
D
1823173
D
4,013.11 held indirectly by ESOP
154,645 held indirectly by Kemper Realty, Inc.
208,080 held indirectly by Pioneer Service Corporation
12,029 held indirectly by Spouse
92,150 held indirectly by Stagecoach Inc.
329,528 held indirectly by Stagecoach Investment, LP
John C. Pauls, by Power of Atty. for R. Crosby Kemper, Jr.
2003-05-27