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

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2009-02-02</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000100885</issuerCik>
        <issuerName>UNION PACIFIC CORP</issuerName>
        <issuerTradingSymbol>UNP</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001200001</rptOwnerCik>
            <rptOwnerName>DUFFY DENNIS J</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>1400 DOUGLAS STREET</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>OMAHA</rptOwnerCity>
            <rptOwnerState>NE</rptOwnerState>
            <rptOwnerZipCode>68179</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>EVP OPS</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <transactionDate>
                <value>2009-02-02</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>F</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>6498</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>42.87</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>188650</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
                <footnoteId id="F2"/>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>163069.1104</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>(1)</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>by Managed Account</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>141332.1147</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>by Trust</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">On May 28, 2008, Union Pacific Corporation effected a 2-for-1 stock split in the form of a stock dividend.  Amounts of securities and the grant price or prices with respect to options, if any, and restricted stock or restricted stock units, if any, reported on this form have been adjusted to reflect the stock split.</footnote>
        <footnote id="F2">Represents conversion of restricted stock units to fully vested stock units with a distribution ratio of 1:1 - Payable only in shares of common stock at termination of employment or a date certain.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>By: Trevor L. Kingston, Attorney-in-Fact  For: Dennis J. Duffy</signatureName>
        <signatureDate>2009-02-04</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0303
4
2009-02-02
0
0000100885
UNION PACIFIC CORP
UNP
0001200001
DUFFY DENNIS J
1400 DOUGLAS STREET
OMAHA
NE
68179
0
1
0
0
EVP OPS
Common Stock
2009-02-02
4
F
0
6498
42.87
D
188650
D
Common Stock
163069.1104
I
(1)
Common Stock
0
I
by Managed Account
Common Stock
141332.1147
I
by Trust
On May 28, 2008, Union Pacific Corporation effected a 2-for-1 stock split in the form of a stock dividend.  Amounts of securities and the grant price or prices with respect to options, if any, and restricted stock or restricted stock units, if any, reported on this form have been adjusted to reflect the stock split.
Represents conversion of restricted stock units to fully vested stock units with a distribution ratio of 1:1 - Payable only in shares of common stock at termination of employment or a date certain.
By: Trevor L. Kingston, Attorney-in-Fact  For: Dennis J. Duffy
2009-02-04