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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2013-03-18</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001200009</rptOwnerCik>
            <rptOwnerName>KNIGHT ROBERT M JR</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 FINANCE &amp; CFO UPC</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <transactionDate>
                <value>2013-03-18</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>20000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>140.5372</value>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>157683</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
                <footnoteId id="F3"/>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>86619.5365</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>(1)</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
                <footnoteId id="F4"/>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>221.7473</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>by Managed Account</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">This transaction was made pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on February 15, 2013. Union Pacific Corporation announced the trading plan in a Current Report on Form 8-K on the same date.</footnote>
        <footnote id="F2">This transaction was executed in multiple trades at prices ranging from $140.09 to $140.90. The price reported above reflects the weighted average sale price. The reporting person hereby undertakes to provide upon request to the SEC staff, the issuer or a security holder of the issuer full information regarding the number of shares and prices at which the transaction was effected.</footnote>
        <footnote id="F3">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>
        <footnote id="F4">Includes holdings in employee benefit plans, Tax Reduction and Payroll Based Stock Plans, as of Transaction Date.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>By: Trevor L. Kingston, Attorney-in-Fact  For: Robert M. Knight, Jr.</signatureName>
        <signatureDate>2013-03-19</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0306
4
2013-03-18
0
0000100885
UNION PACIFIC CORP
UNP
0001200009
KNIGHT ROBERT M JR
1400 DOUGLAS STREET
OMAHA
NE
68179
0
1
0
0
EVP FINANCE & CFO UPC
Common Stock
2013-03-18
4
S
0
20000
140.5372
D
157683
D
Common Stock
86619.5365
I
(1)
Common Stock
221.7473
I
by Managed Account
This transaction was made pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on February 15, 2013. Union Pacific Corporation announced the trading plan in a Current Report on Form 8-K on the same date.
This transaction was executed in multiple trades at prices ranging from $140.09 to $140.90. The price reported above reflects the weighted average sale price. The reporting person hereby undertakes to provide upon request to the SEC staff, the issuer or a security holder of the issuer full information regarding the number of shares and prices at which the transaction was effected.
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.
Includes holdings in employee benefit plans, Tax Reduction and Payroll Based Stock Plans, as of Transaction Date.
By: Trevor L. Kingston, Attorney-in-Fact  For: Robert M. Knight, Jr.
2013-03-19