<?xml version="1.0" encoding="UTF-8"?><edgarSubmission xmlns="http://www.sec.gov/edgar/ownership" xmlns:ns2="http://www.sec.gov/edgar/common">
    <headerData>
        <submissionType>144</submissionType>
        <filerInfo>
            <filer>
                <filerCredentials>
                    <cik>0001648096</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>JOHN R PINION</nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>
            <relationshipsToIssuer>
                <relationshipToIssuer>Officer</relationshipToIssuer>
            </relationshipsToIssuer>
        </issuerInfo>
        <securitiesInformation>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <brokerOrMarketmakerDetails>
                <name>Morgan Stanley Smith Barney LLC</name>
                <address>
                    <ns2:street1>1 New York Plaza</ns2:street1>
                    <ns2:street2>38th Floor</ns2:street2>
                    <ns2:city>New York</ns2:city>
                    <ns2:stateOrCountry>NY</ns2:stateOrCountry>
                    <ns2:zipCode>10004</ns2:zipCode>
                </address>
            </brokerOrMarketmakerDetails>
            <noOfUnitsSold>2012</noOfUnitsSold>
            <aggregateMarketValue>100600.00</aggregateMarketValue>
            <noOfUnitsOutstanding>70814462</noOfUnitsOutstanding>
            <approxSaleDate>05/18/2023</approxSaleDate>
            <securitiesExchangeName>NASD</securitiesExchangeName>
        </securitiesInformation>
        <securitiesToBeSold>
            <securitiesClassTitle>COMMON</securitiesClassTitle>
            <acquiredDate>07/16/2018</acquiredDate>
            <natureOfAcquisitionTransaction>Restricted Stock</natureOfAcquisitionTransaction>
            <nameOfPersonfromWhomAcquired>ISSUER</nameOfPersonfromWhomAcquired>
            <isGiftTransaction>N</isGiftTransaction>
            <amountOfSecuritiesAcquired>786</amountOfSecuritiesAcquired>
            <paymentDate>07/16/2018</paymentDate>
            <natureOfPayment>Not Applicable</natureOfPayment>
        </securitiesToBeSold>
        <securitiesToBeSold>
            <securitiesClassTitle>COMMON</securitiesClassTitle>
            <acquiredDate>07/16/2019</acquiredDate>
            <natureOfAcquisitionTransaction>Restricted Stock</natureOfAcquisitionTransaction>
            <nameOfPersonfromWhomAcquired>ISSUER</nameOfPersonfromWhomAcquired>
            <isGiftTransaction>N</isGiftTransaction>
            <amountOfSecuritiesAcquired>1226</amountOfSecuritiesAcquired>
            <paymentDate>07/16/2019</paymentDate>
            <natureOfPayment>Not Applicable</natureOfPayment>
        </securitiesToBeSold>
        <nothingToReportFlagOnSecuritiesSoldInPast3Months>N</nothingToReportFlagOnSecuritiesSoldInPast3Months>
        <securitiesSoldInPast3Months>
            <sellerDetails>
                <name>JOHN R PINION</name>
                <address>
                    <ns2:street1>60 Leveroni Court</ns2:street1>
                    <ns2:city>Novato</ns2:city>
                    <ns2:stateOrCountry>CA</ns2:stateOrCountry>
                    <ns2:zipCode>94949</ns2:zipCode>
                </address>
            </sellerDetails>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <saleDate>03/01/2023</saleDate>
            <amountOfSecuritiesSold>3755</amountOfSecuritiesSold>
            <grossProceeds>169951.00</grossProceeds>
        </securitiesSoldInPast3Months>
        <noticeSignature>
            <noticeDate>05/18/2023</noticeDate>
            <planAdoptionDates>
                <planAdoptionDate>02/25/2023</planAdoptionDate>
            </planAdoptionDates>
            <signature>/s/ John Richard Pinion</signature>
        </noticeSignature>
    </formData>
</edgarSubmission>
[{"type": "144", "sequence": "1", "filename": "primary_doc.xml", "secsgml_size_bytes": 4560}]
144
0001648096
XXXXXXXX
LIVE
0001515673
ULTRAGENYX PHARMACEUTICAL INC.
001-36276
60 Leveroni Court
Novato
CA
94949
(415) 483-8800
JOHN R PINION
Officer
Common
Morgan Stanley Smith Barney LLC
1 New York Plaza
38th Floor
New York
NY
10004
2012
100600.00
70814462
05/18/2023
NASD
COMMON
07/16/2018
Restricted Stock
ISSUER
N
786
07/16/2018
Not Applicable
COMMON
07/16/2019
Restricted Stock
ISSUER
N
1226
07/16/2019
Not Applicable
N
JOHN R PINION
60 Leveroni Court
Novato
CA
94949
Common
03/01/2023
3755
169951.00
05/18/2023
02/25/2023
/s/ John Richard Pinion