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        <submissionType>144</submissionType>
        <filerInfo>
            <filer>
                <filerCredentials>
                    <cik>0001677455</cik>
                    <ccc>XXXXXXXX</ccc>
                </filerCredentials>
            </filer>
            <liveTestFlag>LIVE</liveTestFlag>



        </filerInfo>
    </headerData>
    <formData>
        <issuerInfo>
            <issuerCik>0001515673</issuerCik>
            <issuerName>ULTRAGENYX PHARMACEUTICAL INC.</issuerName>
            <secFileNumber>001-36276</secFileNumber>
            <issuerAddress>
                <ns2:street1>60 Leveroni Court</ns2:street1>
                <ns2:city>Novato</ns2:city>
                <ns2:stateOrCountry>CA</ns2:stateOrCountry>
                <ns2:zipCode>94949</ns2:zipCode>
            </issuerAddress>
            <issuerContactPhone>(415) 483-8800</issuerContactPhone>
            <nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>KARAH PARSCHAUER</nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>
            <relationshipsToIssuer>
                <relationshipToIssuer>Officer</relationshipToIssuer>
            </relationshipsToIssuer>
        </issuerInfo>
        <securitiesInformation>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <brokerOrMarketmakerDetails>
                <name>Morgan Stanley Smith Barney LLC Executive Financial Services</name>
                <address>
                    <ns2:street1>1 New York Plaza</ns2:street1>
                    <ns2:street2>8th Floor</ns2:street2>
                    <ns2:city>New York</ns2:city>
                    <ns2:stateOrCountry>NY</ns2:stateOrCountry>
                    <ns2:zipCode>10004</ns2:zipCode>
                </address>
            </brokerOrMarketmakerDetails>
            <noOfUnitsSold>9806</noOfUnitsSold>
            <aggregateMarketValue>441270.00</aggregateMarketValue>
            <noOfUnitsOutstanding>83133341</noOfUnitsOutstanding>
            <approxSaleDate>06/12/2024</approxSaleDate>
            <securitiesExchangeName>NASDAQ</securitiesExchangeName>
        </securitiesInformation>
        <securitiesToBeSold>
            <securitiesClassTitle>COMMON</securitiesClassTitle>
            <acquiredDate>03/01/2023</acquiredDate>
            <natureOfAcquisitionTransaction>Restricted Stock</natureOfAcquisitionTransaction>
            <nameOfPersonfromWhomAcquired>ISSUER</nameOfPersonfromWhomAcquired>
            <isGiftTransaction>N</isGiftTransaction>
            <amountOfSecuritiesAcquired>6163</amountOfSecuritiesAcquired>
            <paymentDate>03/01/2023</paymentDate>
            <natureOfPayment>Not Applicable</natureOfPayment>
        </securitiesToBeSold>
        <securitiesToBeSold>
            <securitiesClassTitle>COMMON</securitiesClassTitle>
            <acquiredDate>03/01/2022</acquiredDate>
            <natureOfAcquisitionTransaction>Restricted Stock</natureOfAcquisitionTransaction>
            <nameOfPersonfromWhomAcquired>ISSUER</nameOfPersonfromWhomAcquired>
            <isGiftTransaction>N</isGiftTransaction>
            <amountOfSecuritiesAcquired>3643</amountOfSecuritiesAcquired>
            <paymentDate>03/01/2022</paymentDate>
            <natureOfPayment>Not Applicable</natureOfPayment>
        </securitiesToBeSold>
        <nothingToReportFlagOnSecuritiesSoldInPast3Months>Y</nothingToReportFlagOnSecuritiesSoldInPast3Months>
        <noticeSignature>
            <noticeDate>06/12/2024</noticeDate>
            <planAdoptionDates>
                <planAdoptionDate>03/05/2024</planAdoptionDate>
            </planAdoptionDates>
            <signature>/s/ Karah Herdman Parschauer</signature>
        </noticeSignature>
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144
0001677455
XXXXXXXX
LIVE
0001515673
ULTRAGENYX PHARMACEUTICAL INC.
001-36276
60 Leveroni Court
Novato
CA
94949
(415) 483-8800
KARAH PARSCHAUER
Officer
Common
Morgan Stanley Smith Barney LLC Executive Financial Services
1 New York Plaza
8th Floor
New York
NY
10004
9806
441270.00
83133341
06/12/2024
NASDAQ
COMMON
03/01/2023
Restricted Stock
ISSUER
N
6163
03/01/2023
Not Applicable
COMMON
03/01/2022
Restricted Stock
ISSUER
N
3643
03/01/2022
Not Applicable
Y
06/12/2024
03/05/2024
/s/ Karah Herdman Parschauer