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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2019-01-14</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001764389</rptOwnerCik>
            <rptOwnerName>Vena Vincenzo 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>CHIEF OPERATING OFFICER</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <transactionDate>
                <value>2019-01-14</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>31192</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0.0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>31192</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Non-Qualified Stock Option (right to buy)</value>
                <footnoteId id="F2"/>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>153.89</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2019-01-14</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>54450</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0.0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2020-01-14</value>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <value>2029-01-14</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>54450</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>54450</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Performance retention unit award with a distribution ratio of 1:1.  On 1/14/2019, the reporting person was granted 15,596 Performance Stock Units at target, 50% of which will be earned on 1/14/2020, and 50% of which will be earned on 1/14/2021.  The amount of shares in column 4, 31,192 units,  is the maximum number of shares that the reporting person is eligible to receive. The actual number of shares paid out at vesting, if any, depends on applicable performance criteria being met.</footnote>
        <footnote id="F2">This option becomes exercisable in two equal installments starting one year from the grant date.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>By: Trevor L. Kingston, Attorney-in-Fact For: Vencenzo J. Vena</signatureName>
        <signatureDate>2019-01-16</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0306
4
2019-01-14
0
0000100885
UNION PACIFIC CORP
UNP
0001764389
Vena Vincenzo J
1400 DOUGLAS STREET
OMAHA
NE
68179
0
1
0
0
CHIEF OPERATING OFFICER
Common Stock
2019-01-14
4
A
0
31192
0.0
A
31192
D
Non-Qualified Stock Option (right to buy)
153.89
2019-01-14
4
A
0
54450
0.0
A
2020-01-14
2029-01-14
Common Stock
54450
54450
D
Performance retention unit award with a distribution ratio of 1:1.  On 1/14/2019, the reporting person was granted 15,596 Performance Stock Units at target, 50% of which will be earned on 1/14/2020, and 50% of which will be earned on 1/14/2021.  The amount of shares in column 4, 31,192 units,  is the maximum number of shares that the reporting person is eligible to receive. The actual number of shares paid out at vesting, if any, depends on applicable performance criteria being met.
This option becomes exercisable in two equal installments starting one year from the grant date.
By: Trevor L. Kingston, Attorney-in-Fact For: Vencenzo J. Vena
2019-01-16