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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2006-07-28</periodOfReport>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001229104</rptOwnerCik>
            <rptOwnerName>GENOVESE PETER J</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>2 S. BROADWAY</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>ST. LOUIS</rptOwnerCity>
            <rptOwnerState>MO</rptOwnerState>
            <rptOwnerZipCode>63102</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Vice Chairman</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2006-07-28</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>4107</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>34.3</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>37576.62</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>25327.81</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>by ESOP</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1230</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>by immediate family</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">On May 30, 2006, the common stock of UMB Financial Corporation split 2-for-1 resulting in additional shares</footnote>
        <footnote id="F3">Reflects ESOP allocations and dispositions that have occurred since the date of the reporting person's last ownership report.</footnote>
        <footnote id="F2">Includes shares acquired through participation in the Dividend Reinvestment Plan</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>John C. Pauls, Attorney in Fact</signatureName>
        <signatureDate>2006-07-28</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0202
4
2006-07-28
0000101382
UMB FINANCIAL CORP
UMBF
0001229104
GENOVESE PETER J
2 S. BROADWAY
ST. LOUIS
MO
63102
0
1
0
0
Vice Chairman
Common Stock
2006-07-28
4
S
0
4107
34.3
D
37576.62
D
Common Stock
25327.81
I
by ESOP
Common Stock
1230
I
by immediate family
On May 30, 2006, the common stock of UMB Financial Corporation split 2-for-1 resulting in additional shares
Reflects ESOP allocations and dispositions that have occurred since the date of the reporting person's last ownership report.
Includes shares acquired through participation in the Dividend Reinvestment Plan
John C. Pauls, Attorney in Fact
2006-07-28