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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2006-09-21</periodOfReport>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001229015</rptOwnerCik>
            <rptOwnerName>PAGE DOUGLAS F</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>1010 GRAND BLVD.</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>KANSAS CITY</rptOwnerCity>
            <rptOwnerState>MO</rptOwnerState>
            <rptOwnerZipCode>64106</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>EVP of Subsidiary</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2006-09-21</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>1018</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>15.175</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>37698.104</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>16459.9941</value>
                    <footnoteId id="F2"/>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By ESOP</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Options (Right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>15.175</value>
                <footnoteId id="F3"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2006-09-21</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>1018</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>15.175</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                    <footnoteId id="F3"/>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F4"/>
            </exerciseDate>
            <expirationDate>
                <value>2006-10-18</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>1018</value>
                    <footnoteId id="F3"/>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </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="F4">Options vest 40% 2 years after the date of grant; 60% 3 years after the date of grant; 80% 4 years after the date of grant; and 100% 4 years 11 months after the date of grant.</footnote>
        <footnote id="F3">The number of shares and price have been adjusted from what was originally reported to reflect a 2-for-1 split of UMB Financial Corporation Stock on May 30, 2006.</footnote>
        <footnote id="F2">Reflects ESOP allocations and dispositions that have occurred since the date of the reporting person's last ownership report.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>John C. Pauls, Attorney in Fact</signatureName>
        <signatureDate>2006-09-21</signatureDate>
    </ownerSignature>
</ownershipDocument>
[{"type": "4", "sequence": "1", "filename": "doc.xml", "description": "PRIMARY DOCUMENT", "secsgml_size_bytes": 6954}]
X0202
4
2006-09-21
0000101382
UMB FINANCIAL CORP
UMBF
0001229015
PAGE DOUGLAS F
1010 GRAND BLVD.
KANSAS CITY
MO
64106
0
1
0
0
EVP of Subsidiary
Common Stock
2006-09-21
4
M
0
1018
15.175
A
37698.104
D
Common Stock
16459.9941
I
By ESOP
Stock Options (Right to buy)
15.175
2006-09-21
4
M
0
1018
15.175
D
2006-10-18
Common Stock
1018
0
D
On May 30, 2006, the common stock of UMB Financial Corporation split 2-for-1 resulting in additional shares
Options vest 40% 2 years after the date of grant; 60% 3 years after the date of grant; 80% 4 years after the date of grant; and 100% 4 years 11 months after the date of grant.
The number of shares and price have been adjusted from what was originally reported to reflect a 2-for-1 split of UMB Financial Corporation Stock on May 30, 2006.
Reflects ESOP allocations and dispositions that have occurred since the date of the reporting person's last ownership report.
John C. Pauls, Attorney in Fact
2006-09-21