<SUBMISSION>
<ACCESSION-NUMBER>0000912057-02-036826
<TYPE>S-8
<PUBLIC-DOCUMENT-COUNT>3
<FILING-DATE>20020925
<EFFECTIVENESS-DATE>20020925
<FILER>
<COMPANY-DATA>
<CONFORMED-NAME>UNITED SECURITY BANCSHARES
<CIK>0001137547
<ASSIGNED-SIC>6021
<IRS-NUMBER>912112732
<STATE-OF-INCORPORATION>CA
<FISCAL-YEAR-END>1231
</COMPANY-DATA>
<FILING-VALUES>
<FORM-TYPE>S-8
<ACT>33
<FILE-NUMBER>333-100078
<FILM-NUMBER>02771910
</FILING-VALUES>
<BUSINESS-ADDRESS>
<STREET1>1525 E SHAW AVENUE
<CITY>FRESO
<STATE>CA
<ZIP>93710
</BUSINESS-ADDRESS>
<MAIL-ADDRESS>
<STREET1>1525 E SHAW AVENUE
<CITY>FRESNO
<STATE>CA
<ZIP>93710
</MAIL-ADDRESS>
</FILER>
<DOCUMENT>
<TYPE>S-8
<SEQUENCE>1
<FILENAME>a2089950zs-8.htm
<DESCRIPTION>S-8
<TEXT>
<HTML>
<HEAD>
<TITLE>
</TITLE>
</HEAD>
<BODY BGCOLOR="#FFFFFF" LINK=BLUE  VLINK=PURPLE>
<BR>
<FONT SIZE=3 ><A HREF="#02SAN1752_1">QuickLinks</A></FONT>
<font size=3> -- Click here to rapidly navigate through this document</font>
<P ALIGN="RIGHT"><FONT SIZE=2><B>Registration No.&nbsp;33-&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </B></FONT></P>

<HR NOSHADE>
<HR NOSHADE>
<P ALIGN="CENTER"><FONT SIZE=5><B>SECURITIES AND EXCHANGE COMMISSION<BR>  </B></FONT><FONT SIZE=2><B>Washington, D.C. 20549  </B></FONT></P>

<HR NOSHADE ALIGN="CENTER" WIDTH="120">
<P ALIGN="CENTER"><FONT SIZE=5><B>FORM S-8<BR>  </B></FONT><FONT SIZE=2><B>Registration Statement<BR>
Under the Securities Act of 1933  </B></FONT></P>

<HR NOSHADE ALIGN="CENTER" WIDTH="120">
<P ALIGN="CENTER"><FONT SIZE=5><B>UNITED SECURITY BANCSHARES<BR>  </B></FONT><FONT SIZE=2>(Exact Name of Registrant as Specified in its Charter) </FONT></P>

<!-- User-specified TAGGED TABLE -->
<TABLE WIDTH="100%" BORDER=0 CELLSPACING=0 CELLPADDING=0>
<TR VALIGN="BOTTOM">
<TD WIDTH="50%" ALIGN="CENTER" VALIGN="TOP"><FONT SIZE=2><B>CALIFORNIA</B></FONT></TD>
<TD WIDTH="50%" ALIGN="CENTER" VALIGN="TOP"><FONT SIZE=2><B>91-2112732</B></FONT></TD>
</TR>
<TR VALIGN="BOTTOM">
<TD WIDTH="50%" ALIGN="CENTER" VALIGN="TOP"><FONT SIZE=2>(State or Other Jurisdiction of Incorporation or Organization)</FONT></TD>
<TD WIDTH="50%" ALIGN="CENTER" VALIGN="TOP"><FONT SIZE=2>(I.R.S. Employer Identification No.)</FONT></TD>
</TR>
</TABLE>
<!-- end of user-specified TAGGED TABLE -->

<P ALIGN="CENTER"><FONT SIZE=2><B>1525 EAST SHAW AVENUE, FRESNO, CALIFORNIA 93710, (559)&nbsp;248-4944<BR>  </B></FONT><FONT SIZE=2>(Address of Principal Executive Offices) </FONT></P>

<P ALIGN="CENTER"><FONT SIZE=2><B>UNITED SECURITY BANCSHARES CASH OR DEFERRED STOCK OWNERSHIP PLAN<BR>  </B></FONT><FONT SIZE=2>(Full Title of the Plans) </FONT></P>

<P ALIGN="CENTER"><FONT SIZE=2><B>DENNIS R. WOODS, PRESIDENT&nbsp;&amp; CEO<BR>
1525 EAST SHAW AVENUE, FRESNO, CALIFORNIA 93710, (559)&nbsp;248-4944<BR>  </B></FONT><FONT SIZE=2>(Name and Address of Agent for Service) </FONT></P>

<P ALIGN="CENTER"><FONT SIZE=2><B>(589)&nbsp;248-4943<BR>  </B></FONT><FONT SIZE=2>(Telephone Number, including Area Code, of Agent for Service) </FONT></P>

<P ALIGN="CENTER"><FONT SIZE=2><B>Copy to:<BR>
Gary Steven Findley, Esq.<BR>
Gary Steven Findley&nbsp;&amp; Associates<BR>
1470 North Hundley Street, Anaheim, California 92806 (714)&nbsp;630-7136  </B></FONT></P>

<HR NOSHADE ALIGN="CENTER" WIDTH="120">
<P ALIGN="CENTER"><FONT SIZE=2><B> CALCULATION OF REGISTRATION FEE  </B></FONT></P>

<!-- User-specified TAGGED TABLE -->
<TABLE WIDTH="100%" BORDER=0 CELLSPACING=0 CELLPADDING=0>
<TR VALIGN="TOP">
<TD COLSPAN=9 VALIGN="BOTTOM"><BR><HR NOSHADE></TD>
</TR>
<TR VALIGN="TOP">
<TD WIDTH="35%" ALIGN="CENTER" VALIGN="BOTTOM"><FONT SIZE=1><B>Title of Each Class Of Securities To Be Registered</B></FONT></TD>
<TD WIDTH="1%" VALIGN="BOTTOM"><FONT SIZE=1>&nbsp;</FONT></TD>
<TD WIDTH="18%" ALIGN="CENTER" VALIGN="BOTTOM"><FONT SIZE=1><B>Amount To Be Registered(a)</B></FONT></TD>
<TD WIDTH="1%" VALIGN="BOTTOM"><FONT SIZE=1>&nbsp;</FONT></TD>
<TD WIDTH="15%" ALIGN="CENTER" VALIGN="BOTTOM"><FONT SIZE=1><B>Proposed Maximum Offering Price Per Share(b)</B></FONT></TD>
<TD WIDTH="1%" VALIGN="BOTTOM"><FONT SIZE=1>&nbsp;</FONT></TD>
<TD WIDTH="15%" ALIGN="CENTER" VALIGN="BOTTOM"><FONT SIZE=1><B>Proposed Maximum Aggregate Offering Price</B></FONT></TD>
<TD WIDTH="1%" VALIGN="BOTTOM"><FONT SIZE=1>&nbsp;</FONT></TD>
<TD WIDTH="15%" ALIGN="CENTER" VALIGN="BOTTOM"><FONT SIZE=1><B>Amount of Registration Fee</B></FONT></TD>
</TR>
<TR VALIGN="TOP">
<TD COLSPAN=9 VALIGN="BOTTOM"><HR NOSHADE></TD>
</TR>
<TR VALIGN="TOP">
<TD WIDTH="35%" VALIGN="BOTTOM"><FONT SIZE=2>Common stock (No Par Value)</FONT></TD>
<TD WIDTH="1%" VALIGN="BOTTOM"><FONT SIZE=2>&nbsp;</FONT></TD>
<TD WIDTH="18%" ALIGN="CENTER" VALIGN="BOTTOM"><FONT SIZE=2>100,000 Shares</FONT></TD>
<TD WIDTH="1%" VALIGN="BOTTOM"><FONT SIZE=2>&nbsp;</FONT></TD>
<TD WIDTH="15%" ALIGN="CENTER" VALIGN="BOTTOM"><FONT SIZE=2>$17.65</FONT></TD>
<TD WIDTH="1%" VALIGN="BOTTOM"><FONT SIZE=2>&nbsp;</FONT></TD>
<TD WIDTH="15%" ALIGN="CENTER" VALIGN="BOTTOM"><FONT SIZE=2>$1,765,000</FONT></TD>
<TD WIDTH="1%" VALIGN="BOTTOM"><FONT SIZE=2>&nbsp;</FONT></TD>
<TD WIDTH="15%" ALIGN="CENTER" VALIGN="BOTTOM"><FONT SIZE=2>$162.38</FONT></TD>
</TR>
<TR VALIGN="TOP">
<TD COLSPAN=9 VALIGN="BOTTOM"><HR NOSHADE></TD>
</TR>
</TABLE>
<!-- end of user-specified TAGGED TABLE -->

<DL compact>
<DT style='margin-bottom:-11pt;'><FONT SIZE=2><B>a)</B></FONT></DT><DD><FONT SIZE=2><B> There are also registered hereby such indeterminate number of shares of common stock as may become issuable by reason of the operation of the anti-dilution or certain other
provisions of the United Security Bancshares Cash or Deferred Stock Ownership Plan.
<BR><BR> </B></FONT></DD><DT style='margin-bottom:-11pt;'><FONT SIZE=2><B>(b)</B></FONT></DT><DD><FONT SIZE=2><B> Estimated pursuant to Rule&nbsp;457(h) solely for the purpose of computing the registration fee, utilizing $17.65 as the average of the bid and asked price of United
Security
Bancshares' common stock as of September&nbsp;20, 2002.  </B></FONT></DD></DL>
<BR>
<HR NOSHADE>
<HR NOSHADE>
<HR NOSHADE>
<!-- ZEQ.=1,SEQ=1,EFW="2089950",CP="UNITED SECURITY BANCSHARES",DN="1",CHK=950811,FOLIO='blank',FILE='DISK030:[02SAN2.02SAN1752]BA1752A.;6',USER='AHUTCHI',CD='25-SEP-2002;12:47' -->
<!-- THIS IS THE END OF A COMPOSITION COMPONENT -->
<P ALIGN="CENTER"><FONT SIZE=2><A
NAME="page_de1752_1_2"> </A> </FONT></P>

<!-- TOC_END -->
<P ALIGN="CENTER"><FONT SIZE=2><A
NAME="de1752_part_ii"> </A>
<A NAME="toc_de1752_1"> </A>
<BR></FONT><FONT SIZE=2><B>PART II    <BR>  </B></FONT></P>

<P><FONT SIZE=2><A
NAME="de1752_item_3._incorporation_of_documents_by_reference"> </A>
<A NAME="toc_de1752_2"> </A></FONT> <FONT SIZE=2><B>Item 3. Incorporation of Documents by Reference    <BR>  </B></FONT></P>


<P><FONT SIZE=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;United Security Bancshares (the "Registrant") hereby incorporates by reference the documents listed below. All documents subsequently filed by the Registrant
pursuant to Sections 13(a), 13(c), 14 and 15(d) of the Securities Exchange Act of 1934 prior to the filing of a post-effective amendment which indicates that all securities offered have
been sold or which deregisters all securities then remaining unsold, shall be deemed to be incorporated by reference herein and to be a part hereof from the date of filing such documents. </FONT></P>

<DL compact>
<DT style='margin-bottom:-11pt;'><FONT SIZE=2>(a)</FONT></DT><DD><FONT SIZE=2>The
Registrant's annual report filed on Form&nbsp;10-K for the year ended December&nbsp;31, 2001.
<BR><BR></FONT></DD><DT style='margin-bottom:-11pt;'><FONT SIZE=2>(b)</FONT></DT><DD><FONT SIZE=2>The
Registrant's quarterly reports filed on Form&nbsp;10-Q for the quarters ended March&nbsp;31, 2002 and June&nbsp;30, 2002.
<BR><BR></FONT></DD><DT style='margin-bottom:-11pt;'><FONT SIZE=2>(c)</FONT></DT><DD><FONT SIZE=2>The
description of the Registrant's common stock is contained in its Registration Statement on Form&nbsp;S-4, file number 333-58256. </FONT></DD></DL>

<P><FONT SIZE=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Any
statement contained herein or in any document incorporated by reference herein shall be deemed to be modified or superseded for purposes of this Registration Statement to the extent
that another statement contained herein or in any other document subsequently filed, which also is incorporated by reference herein, modifies or supersedes such statement. Any statement so modified or
superseded shall not be deemed, except as so modified or superseded, to constitute a part of this Registration Statement. </FONT></P>

<P><FONT SIZE=2><A
NAME="de1752_item_4._description_of_securities"> </A>
<A NAME="toc_de1752_3"> </A>
<BR></FONT><FONT SIZE=2><B>Item 4. Description of Securities    <BR>  </B></FONT></P>

<P><FONT SIZE=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Not Applicable. </FONT></P>


<P><FONT SIZE=2><A
NAME="de1752_item_5._interests_of_named_experts_and_counsel"> </A>
<A NAME="toc_de1752_4"> </A>
<BR></FONT><FONT SIZE=2><B>Item 5. Interests of Named Experts and Counsel    <BR>  </B></FONT></P>

<P><FONT SIZE=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Not Applicable. </FONT></P>

<P><FONT SIZE=2><A
NAME="de1752_item_6._indemnification_of_directors_and_officers"> </A>
<A NAME="toc_de1752_5"> </A>
<BR></FONT><FONT SIZE=2><B>Item 6. Indemnification of Directors and Officers    <BR>  </B></FONT></P>

<P><FONT SIZE=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;The Articles of Incorporation and Bylaws of United Security Bancshares ("Registrant") provide for indemnification of agents including directors, officers and
employees to the maximum extent allowed by California law including the use of an indemnity agreement. Registrant's Articles further provide for the elimination of director liability for monetary
damages to the maximum extent allowed by California law. The indemnification law of the State of California generally allows indemnification in matters not involving the right of the corporation, to
an agent of the corporation if such person acted in good faith and in a manner such person reasonably believed to be in the best interests of the corporation, and in the case of a criminal matter, had
no reasonable cause to believe the conduct of such person was unlawful. California law, with respect to matters involving the right of a corporation, allows indemnification of an agent of the
corporation, if such person acted in good faith, in a manner such person believed to be in the best interests of the corporation and its shareholders; provided that there shall be no indemnification
for: (i)&nbsp;amounts paid in settling or otherwise disposing of a pending action without court approval; (ii)&nbsp;expenses incurred in defending a pending action which is settled or otherwise
disposed of without court approval; (iii)&nbsp;matters in which such person shall have been adjudged to be liable to the corporation unless and only to the extent that the court in which the
proceeding is or was pending shall determine that such person is entitled to be indemnified; or (iv)&nbsp;other matters specified in the California General Corporation Law. </FONT></P>

<P><FONT SIZE=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Registrant's
Bylaws provide that Registrant shall to the maximum extent permitted by law have the power to indemnify its directors, officers and employees. Registrant's Bylaws also
provide that </FONT></P>

<P ALIGN="CENTER"><FONT SIZE=2>2</FONT></P>

<HR NOSHADE>
<!-- ZEQ.=1,SEQ=2,EFW="2089950",CP="UNITED SECURITY BANCSHARES",DN="1",CHK=461851,FOLIO='2',FILE='DISK030:[02SAN2.02SAN1752]DE1752A.;3',USER='ILEONG',CD='24-SEP-2002;22:14' -->
<A NAME="page_de1752_1_3"> </A>
<BR>

<P><FONT SIZE=2>
Registrant shall have the power to purchase and maintain insurance covering its directors, officers and employees against any liability asserted against any of them and incurred by any of them,
whether or not Registrant would have the power to indemnify them against such liability under the provisions of applicable law or the provisions of Registrant's Bylaws. </FONT></P>

<P><FONT SIZE=2><A
NAME="de1752_item_7._exemption_from_registration_claimed"> </A>
<A NAME="toc_de1752_6"> </A>
<BR></FONT><FONT SIZE=2><B>Item 7. Exemption from Registration Claimed    <BR>  </B></FONT></P>


<P><FONT SIZE=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Not Applicable. </FONT></P>

<P><FONT SIZE=2><A
NAME="de1752_item_8._exhibits"> </A>
<A NAME="toc_de1752_7"> </A>
<BR></FONT><FONT SIZE=2><B>Item 8. Exhibits    <BR>  </B></FONT></P>

<!-- User-specified TAGGED TABLE -->
<TABLE WIDTH="100%" BORDER=0 CELLSPACING=0 CELLPADDING=0>
<TR VALIGN="TOP">
<TD WIDTH="6%" ALIGN="RIGHT"><FONT SIZE=2>5.1</FONT></TD>
<TD WIDTH="3%"><FONT SIZE=2>&nbsp;</FONT></TD>
<TD WIDTH="92%"><FONT SIZE=2>Opinion re: Legality</FONT></TD>
</TR>
<TR VALIGN="TOP">
<TD WIDTH="6%" ALIGN="RIGHT"><FONT SIZE=2>&nbsp;</FONT></TD>
<TD WIDTH="3%"><FONT SIZE=2>&nbsp;</FONT></TD>
<TD WIDTH="92%"><FONT SIZE=2>Favorable determination letter from the Internal Revenue Service for the United Security Bancshares Cash or Deferred Stock Ownership Plan.</FONT></TD>
</TR>
<TR VALIGN="TOP">
<TD WIDTH="6%" ALIGN="RIGHT"><FONT SIZE=2>23.1</FONT></TD>
<TD WIDTH="3%"><FONT SIZE=2>&nbsp;</FONT></TD>
<TD WIDTH="92%"><FONT SIZE=2>Consent of Moss Adams LLP</FONT></TD>
</TR>
</TABLE>
<!-- end of user-specified TAGGED TABLE -->


<P><FONT SIZE=2><A
NAME="de1752_item_9._undertakings"> </A>
<A NAME="toc_de1752_8"> </A>
<BR></FONT><FONT SIZE=2><B>Item 9. Undertakings    <BR>  </B></FONT></P>

<P><FONT SIZE=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;The undersigned Registrant hereby undertakes: </FONT></P>

<DL compact>
<DT style='margin-bottom:-11pt;'><FONT SIZE=2>(1)</FONT></DT><DD><FONT SIZE=2>To
file, during any period in which offers or sales are being made, a post-effective amendment to this Registration Statement:
<BR><BR></FONT>
<DL compact>
<DT style='margin-bottom:-11pt;'><FONT SIZE=2>(i)</FONT></DT><DD><FONT SIZE=2>To
include any prospectus required by Section&nbsp;10(a)(3) of the Securities Act of 1933;
<BR><BR></FONT></DD><DT style='margin-bottom:-11pt;'><FONT SIZE=2>(ii)</FONT></DT><DD><FONT SIZE=2>To
reflect in the prospectus any facts or events arising after the effective date of the Registration Statement (or the most recent
post-effective amendment thereof) which, individually or in the aggregate, represent a fundamental change in the information set forth in the Registration Statement;
<BR><BR></FONT></DD><DT style='margin-bottom:-11pt;'><FONT SIZE=2>(iii)</FONT></DT><DD><FONT SIZE=2>To
include any material information with respect to the plan of distribution not previously disclosed in the Registration Statement or any material
change to such information in the Registration Statement; </FONT></DD></DL>
</DD></DL>
<UL>

<P><FONT SIZE=2>provided,
however, that paragraphs (1)(i)&nbsp;and (1)(ii)&nbsp;do not apply if the Registration Statement is on Form&nbsp;S-3 or Form&nbsp;S-8 and the information
required to be included in a post-effective amendment by those paragraphs is contained in periodic reports filed with or furnished to the Commission by the Registrant pursuant to
Section&nbsp;13 or Section&nbsp;15(d) of the Securities Exchange Act of 1934 that are incorporated by reference in the Registration Statement. </FONT></P>

</UL>
<DL compact>
<DT style='margin-bottom:-11pt;'><FONT SIZE=2>(2)</FONT></DT><DD><FONT SIZE=2>That,
for the purpose of determining any liability under the Securities Act of 1933, each such post-effective amendment shall be deemed to be a new registration statement
relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.
<BR><BR></FONT></DD><DT style='margin-bottom:-11pt;'><FONT SIZE=2>(3)</FONT></DT><DD><FONT SIZE=2>To
remove from registration by means of a post-effective amendment any of the securities being registered which remain unsold at the termination of the offering. </FONT></DD></DL>

<P><FONT SIZE=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;The
undersigned Registrant hereby undertakes that, for purposes of determining any liability under the Securities Act of 1933, each filing of the Registrant's annual report pursuant to
Section&nbsp;13(a) or Section&nbsp;15(d) of the Securities Exchange Act of 1934 (and, where applicable, each filing of an employee benefit plan's annual report pursuant to Section&nbsp;15(d) of
the Securities Exchange Act of 1934) that is incorporated by reference in the Registration Statement shall be deemed to be a new registration statement relating to the securities offered therein, and
the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof. </FONT></P>

<P ALIGN="CENTER"><FONT SIZE=2>3</FONT></P>

<HR NOSHADE>
<!-- ZEQ.=2,SEQ=3,EFW="2089950",CP="UNITED SECURITY BANCSHARES",DN="1",CHK=1039322,FOLIO='3',FILE='DISK030:[02SAN2.02SAN1752]DE1752A.;3',USER='ILEONG',CD='24-SEP-2002;22:14' -->
<A NAME="page_de1752_1_4"> </A>
<BR>

<P><FONT SIZE=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Insofar
as indemnification for liabilities arising under the Securities Act of 1933 may be permitted to directors, officers and controlling persons of the Registrant pursuant to the
foregoing provisions, or otherwise, the Registrant has been advised that in the opinion of the Securities and Exchange Commission such indemnification is against public policy as expressed in the Act
and is, therefore, unenforceable. In the event that a claim for indemnification against such liabilities (other than the payment by the Registrant of expenses incurred or paid by a director, officer
or controlling person of the Registrant in the successful defense of any action, suit or proceeding) is asserted by such director, officer or controlling person in connection with the securities being
registered, the Registrant will, unless in the opinion of its counsel the matter has been settled by controlling precedent, submit to a court of appropriate jurisdiction the question whether such
indemnification by it is against public policy as expressed in the Act and will be governed by the final adjudication of such issue. </FONT></P>

<P ALIGN="CENTER"><FONT SIZE=2>4</FONT></P>

<HR NOSHADE>
<!-- ZEQ.=3,SEQ=4,EFW="2089950",CP="UNITED SECURITY BANCSHARES",DN="1",CHK=974696,FOLIO='4',FILE='DISK030:[02SAN2.02SAN1752]DE1752A.;3',USER='ILEONG',CD='24-SEP-2002;22:14' -->
<BR>
<!-- THIS IS THE END OF A COMPOSITION COMPONENT -->
<P ALIGN="CENTER"><FONT SIZE=2><A
NAME="page_jc1752_1_5"> </A> </FONT></P>

<!-- TOC_END -->
<P ALIGN="CENTER"><FONT SIZE=2><A
NAME="jc1752_signatures"> </A>
<A NAME="toc_jc1752_1"> </A>
<BR></FONT><FONT SIZE=2><B>SIGNATURES    <BR>  </B></FONT></P>

<P><FONT SIZE=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Pursuant to the requirements of the Securities Act of 1933, the Registrant certifies that it has reasonable grounds to believe that it meets all of the
requirements for filing on Form&nbsp;S-8 and has duly caused this Registration Statement to be signed on its behalf by the undersigned, thereunto duly the City of Fresno, California, on
September&nbsp;24, 2002. </FONT></P>

<!-- User-specified TAGGED TABLE -->
<TABLE WIDTH="100%" BORDER=0 CELLSPACING=0 CELLPADDING=0>
<TR VALIGN="TOP">
<TD WIDTH="49%"><FONT SIZE=2>&nbsp;</FONT></TD>
<TD WIDTH="3%"><FONT SIZE=2>&nbsp;</FONT></TD>
<TD WIDTH="49%"><FONT SIZE=2><B>United Security Bancshares</B></FONT></TD>
</TR>
<TR VALIGN="TOP">
<TD WIDTH="49%"><FONT SIZE=2><BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</FONT></TD>
<TD WIDTH="3%"><FONT SIZE=2><BR>&nbsp;</FONT></TD>
<TD WIDTH="49%"><FONT SIZE=2><BR>
&nbsp;</FONT></TD>
</TR>
<TR VALIGN="TOP">
<TD WIDTH="49%"><FONT SIZE=2><BR>
&nbsp;</FONT></TD>
<TD WIDTH="3%"><FONT SIZE=2><BR>&nbsp;</FONT></TD>
<TD WIDTH="49%"><FONT SIZE=2><BR>
/s/&nbsp;&nbsp;</FONT><FONT SIZE=2>DENNIS R. WOODS</FONT><FONT SIZE=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</FONT><HR NOSHADE><FONT SIZE=2> Dennis R. Woods, President&nbsp;&amp; CEO</FONT></TD>
</TR>
</TABLE>
<!-- end of user-specified TAGGED TABLE -->


<P><FONT SIZE=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Pursuant
to the requirements of the Securities Act of 1933, this Registration Statement has been signed by the following persons in the capacities and on the date indicated. </FONT></P>

<!-- User-specified TAGGED TABLE -->
<TABLE WIDTH="82%" BORDER=0 CELLSPACING=0 CELLPADDING=0>
<TR VALIGN="TOP">
<TD WIDTH="37%"><FONT SIZE=2>/s/&nbsp;&nbsp;</FONT><FONT SIZE=2>DENNIS R. WOODS</FONT><FONT SIZE=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</FONT><HR NOSHADE><FONT SIZE=2> Dennis R. Woods</FONT></TD>
<TD WIDTH="37%"><FONT SIZE=2>, Chairman and Principal Executive Officer</FONT></TD>
<TD WIDTH="2%"><FONT SIZE=2>&nbsp;</FONT></TD>
<TD WIDTH="24%"><FONT SIZE=2>September&nbsp;24, 2002</FONT></TD>
</TR>
<TR VALIGN="TOP">
<TD WIDTH="37%"><FONT SIZE=2><BR>
/s/&nbsp;&nbsp;</FONT><FONT SIZE=2>ROBERT G. BITTER</FONT><FONT SIZE=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</FONT><HR NOSHADE><FONT SIZE=2> Robert G. Bitter, Pharm. D.</FONT></TD>
<TD WIDTH="37%"><FONT SIZE=2><BR>
, Director and Secretary</FONT></TD>
<TD WIDTH="2%"><FONT SIZE=2><BR>&nbsp;</FONT></TD>
<TD WIDTH="24%"><FONT SIZE=2><BR>
September&nbsp;24, 2002</FONT></TD>
</TR>
<TR VALIGN="TOP">
<TD WIDTH="37%"><FONT SIZE=2><BR>
/s/&nbsp;&nbsp;</FONT><FONT SIZE=2>STANLEY J. CAVALLA</FONT><FONT SIZE=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</FONT><HR NOSHADE><FONT SIZE=2> Stanley J. Cavalla</FONT></TD>
<TD WIDTH="37%"><FONT SIZE=2><BR>
, Director</FONT></TD>
<TD WIDTH="2%"><FONT SIZE=2><BR>&nbsp;</FONT></TD>
<TD WIDTH="24%"><FONT SIZE=2><BR>
September&nbsp;24, 2002</FONT></TD>
</TR>
<TR VALIGN="TOP">
<TD WIDTH="37%"><FONT SIZE=2><BR>
/s/&nbsp;&nbsp;</FONT><FONT SIZE=2>TOM ELLITHORPE</FONT><FONT SIZE=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</FONT><HR NOSHADE><FONT SIZE=2> Tom Ellithorpe</FONT></TD>
<TD WIDTH="37%"><FONT SIZE=2><BR>
, Director</FONT></TD>
<TD WIDTH="2%"><FONT SIZE=2><BR>&nbsp;</FONT></TD>
<TD WIDTH="24%"><FONT SIZE=2><BR>
September&nbsp;24, 2002</FONT></TD>
</TR>
<TR VALIGN="TOP">
<TD WIDTH="37%"><FONT SIZE=2><BR>
/s/&nbsp;&nbsp;</FONT><FONT SIZE=2>RONNIE D. MILLER</FONT><FONT SIZE=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</FONT><HR NOSHADE><FONT SIZE=2> Ronnie D. Miller</FONT></TD>
<TD WIDTH="37%"><FONT SIZE=2><BR>
, Vice Chairman</FONT></TD>
<TD WIDTH="2%"><FONT SIZE=2><BR>&nbsp;</FONT></TD>
<TD WIDTH="24%"><FONT SIZE=2><BR>
September&nbsp;24, 2002</FONT></TD>
</TR>
<TR VALIGN="BOTTOM">
<TD WIDTH="37%" VALIGN="TOP"><BR><HR NOSHADE><FONT SIZE=2> Mike Munoz, Jr.</FONT></TD>
<TD WIDTH="37%" VALIGN="TOP"><FONT SIZE=2><BR>
, Director</FONT></TD>
<TD WIDTH="2%" VALIGN="TOP"><FONT SIZE=2><BR>&nbsp;</FONT></TD>
<TD WIDTH="24%"><FONT SIZE=2><BR>
&nbsp;</FONT></TD>
</TR>
<TR VALIGN="TOP">
<TD WIDTH="37%"><FONT SIZE=2><BR>
/s/&nbsp;&nbsp;</FONT><FONT SIZE=2>WALTER REINHARD</FONT><FONT SIZE=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</FONT><HR NOSHADE><FONT SIZE=2> Walter Reinhard</FONT></TD>
<TD WIDTH="37%"><FONT SIZE=2><BR>
, Director</FONT></TD>
<TD WIDTH="2%"><FONT SIZE=2><BR>&nbsp;</FONT></TD>
<TD WIDTH="24%"><FONT SIZE=2><BR>
September&nbsp;24, 2002</FONT></TD>
</TR>
<TR VALIGN="TOP">
<TD WIDTH="37%"><FONT SIZE=2><BR>
/s/&nbsp;&nbsp;</FONT><FONT SIZE=2>JOHN TERZIAN</FONT><FONT SIZE=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</FONT><HR NOSHADE><FONT SIZE=2> John Terzian</FONT></TD>
<TD WIDTH="37%"><FONT SIZE=2><BR>
, Director</FONT></TD>
<TD WIDTH="2%"><FONT SIZE=2><BR>&nbsp;</FONT></TD>
<TD WIDTH="24%"><FONT SIZE=2><BR>
September&nbsp;24, 2002</FONT></TD>
</TR>
<TR VALIGN="TOP">
<TD WIDTH="37%"><FONT SIZE=2><BR>
/s/&nbsp;&nbsp;</FONT><FONT SIZE=2>BOBBI THOMASON</FONT><FONT SIZE=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</FONT><HR NOSHADE><FONT SIZE=2> Bobbi Thomason</FONT></TD>
<TD WIDTH="37%"><FONT SIZE=2><BR>
, Director</FONT></TD>
<TD WIDTH="2%"><FONT SIZE=2><BR>&nbsp;</FONT></TD>
<TD WIDTH="24%"><FONT SIZE=2><BR>
September&nbsp;24, 2002</FONT></TD>
</TR>
<TR VALIGN="TOP">
<TD WIDTH="37%"><FONT SIZE=2><BR>
/s/&nbsp;&nbsp;</FONT><FONT SIZE=2>KENNETH L. DONAHUE</FONT><FONT SIZE=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</FONT><HR NOSHADE><FONT SIZE=2> Kenneth L. Donahue</FONT></TD>
<TD WIDTH="37%"><FONT SIZE=2><BR>
, Principal Accounting&nbsp;&amp; Financial Officer</FONT></TD>
<TD WIDTH="2%"><FONT SIZE=2><BR>&nbsp;</FONT></TD>
<TD WIDTH="24%"><FONT SIZE=2><BR>
September&nbsp;24, 2002</FONT></TD>
</TR>
</TABLE>
<!-- end of user-specified TAGGED TABLE -->

<P ALIGN="CENTER"><FONT SIZE=2>5</FONT></P>

<HR NOSHADE>
<!-- ZEQ.=1,SEQ=5,EFW="2089950",CP="UNITED SECURITY BANCSHARES",DN="1",CHK=955974,FOLIO='5',FILE='DISK030:[02SAN2.02SAN1752]JC1752A.;10',USER='ILEONG',CD='24-SEP-2002;22:14' -->
<!-- THIS IS THE END OF A COMPOSITION COMPONENT -->
<!-- TOC_END -->
<P ALIGN="CENTER"><FONT SIZE=2><A
NAME="ka1752_exhibit_index"> </A>
<A NAME="toc_ka1752_1"> </A>
<BR></FONT><FONT SIZE=2><B>EXHIBIT INDEX    <BR>  </B></FONT></P>

<!-- User-specified TAGGED TABLE -->
<TABLE WIDTH="79%" BORDER=0 CELLSPACING=0 CELLPADDING=0>
<TR VALIGN="BOTTOM">
<TH WIDTH="10%" ALIGN="CENTER"><FONT SIZE=1><B>Exhibit<BR>
Number</B></FONT><HR NOSHADE></TH>
<TH WIDTH="3%"><FONT SIZE=1>&nbsp;</FONT></TH>
<TH WIDTH="88%" ALIGN="LEFT"><FONT SIZE=1><B>Description<BR> </B></FONT><HR NOSHADE></TH>
</TR>
<TR VALIGN="TOP">
<TD WIDTH="10%" ALIGN="RIGHT"><FONT SIZE=2><BR>
5.1</FONT></TD>
<TD WIDTH="3%"><FONT SIZE=2><BR>&nbsp;</FONT></TD>
<TD WIDTH="88%"><FONT SIZE=2><BR>
Opinion re: Legality IRS Favorable Determination Letter</FONT></TD>
</TR>
<TR VALIGN="TOP">
<TD WIDTH="10%" ALIGN="RIGHT"><FONT SIZE=2><BR>
23.1</FONT></TD>
<TD WIDTH="3%"><FONT SIZE=2><BR>&nbsp;</FONT></TD>
<TD WIDTH="88%"><FONT SIZE=2><BR>
Consent of Moss Adams LLP</FONT></TD>
</TR>
</TABLE>
<!-- end of user-specified TAGGED TABLE -->

<HR NOSHADE>
<!-- ZEQ.=1,SEQ=6,EFW="2089950",CP="UNITED SECURITY BANCSHARES",DN="1",CHK=912412,FOLIO='blank',FILE='DISK030:[02SAN2.02SAN1752]KA1752A.;3',USER='ILEONG',CD='24-SEP-2002;22:14' -->
<!-- THIS IS THE END OF A COMPOSITION COMPONENT -->
<BR>
<P><br><A NAME="02SAN1752_1">QuickLinks</A><br></P><!-- TOC_BEGIN -->
<FONT SIZE=2><A HREF="#toc_de1752_1">PART II</A></FONT><BR>
<UL>
<FONT SIZE=2><A HREF="#toc_de1752_2">Item 3. Incorporation of Documents by Reference</A></FONT><BR>
<FONT SIZE=2><A HREF="#toc_de1752_3">Item 4. Description of Securities</A></FONT><BR>
<FONT SIZE=2><A HREF="#toc_de1752_4">Item 5. Interests of Named Experts and Counsel</A></FONT><BR>
<FONT SIZE=2><A HREF="#toc_de1752_5">Item 6. Indemnification of Directors and Officers</A></FONT><BR>
<FONT SIZE=2><A HREF="#toc_de1752_6">Item 7. Exemption from Registration Claimed</A></FONT><BR>
<FONT SIZE=2><A HREF="#toc_de1752_7">Item 8. Exhibits</A></FONT><BR>
<FONT SIZE=2><A HREF="#toc_de1752_8">Item 9. Undertakings</A></FONT><BR>
</UL>
<!-- TOC_BEGIN -->
<FONT SIZE=2><A HREF="#toc_jc1752_1">SIGNATURES</A></FONT><BR>
<!-- TOC_BEGIN -->
<FONT SIZE=2><A HREF="#toc_ka1752_1">EXHIBIT INDEX</A></FONT><BR>
<!-- SEQ=,FILE='QUICKLINK',USER=SFLORES,SEQ=,EFW="2089950",CP="UNITED SECURITY BANCSHARES",DN="1" -->
<!-- TOCEXISTFLAG -->
</BODY>
</HTML>

</TEXT>
</DOCUMENT>
<DOCUMENT>
<TYPE>EX-5.1
<SEQUENCE>3
<FILENAME>a2089950zex-5_1.htm
<DESCRIPTION>EXHIBIT 5.1
<TEXT>
<HTML>
<HEAD>
<TITLE>
</TITLE>
</HEAD>
<BODY BGCOLOR="#FFFFFF" LINK=BLUE  VLINK=PURPLE>
<BR>
<FONT SIZE=3 ><A HREF="#02SAN1752_2">QuickLinks</A></FONT>
<font size=3> -- Click here to rapidly navigate through this document</font>
<!-- TOC_END -->
<P ALIGN="CENTER"><FONT SIZE=2><A
NAME="ke1752_exhibit_5.1"> </A>
<A NAME="toc_ke1752_1"> </A>
<BR></FONT><FONT SIZE=2><B>EXHIBIT 5.1    <BR>  </B></FONT></P>

<P ALIGN="CENTER"><FONT SIZE=2><B>OPINION RE: LEGALITY<BR>
IRS FAVORABLE DETERMINATION LETTER  </B></FONT></P>

<HR NOSHADE>
<!-- ZEQ.=1,SEQ=1,EFW="2089950",CP="UNITED SECURITY BANCSHARES",DN="2",CHK=45544,FOLIO='blank',FILE='DISK030:[02SAN2.02SAN1752]KE1752A.;7',USER='ILEONG',CD='24-SEP-2002;22:14' -->

<!-- User-specified TAGGED TABLE -->
<TABLE WIDTH="100%" BORDER=0 CELLSPACING=0 CELLPADDING=0>
<TR VALIGN="BOTTOM">
<TD WIDTH="49%" VALIGN="TOP"><FONT SIZE=2><B>INTERNAL REVENUE SERVICE<BR>
DISTRICT DIRECTOR<BR>
2 CUPANIA CIRCLE<BR>
MONTEREY PARK, CA 91755</B></FONT></TD>
<TD WIDTH="3%" VALIGN="TOP"><FONT SIZE=2>&nbsp;</FONT></TD>
<TD WIDTH="49%" VALIGN="TOP"><FONT SIZE=2><B>DEPARTMENT OF THE TREASURY</B></FONT></TD>
</TR>
<TR VALIGN="TOP">
<TD WIDTH="49%"><FONT SIZE=2><B><BR>
Date: December&nbsp;12, 1995</B></FONT></TD>
<TD WIDTH="3%"><FONT SIZE=2><B><BR>&nbsp;</B></FONT></TD>
<TD WIDTH="49%"><FONT SIZE=2><B><BR>
Employer Identification Number:<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;77-0103429</B></FONT></TD>
</TR>
<TR VALIGN="TOP">
<TD WIDTH="49%"><FONT SIZE=2>&nbsp;</FONT></TD>
<TD WIDTH="3%"><FONT SIZE=2>&nbsp;</FONT></TD>
<TD WIDTH="49%"><FONT SIZE=2><B>File Folder Number:<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;771008604</B></FONT></TD>
</TR>
<TR VALIGN="TOP">
<TD WIDTH="49%"><FONT SIZE=2><B>UNITED SECURITY BANK, N.A.<BR>
2151 W. SHAW AVENUE<BR>
FRESNO, CA 93711</B></FONT></TD>
<TD WIDTH="3%"><FONT SIZE=2>&nbsp;</FONT></TD>
<TD WIDTH="49%"><FONT SIZE=2><B>Person to Contact:<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;CORENE MORTON<BR>
Contact Telephone Number:<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(714)&nbsp;643-4231</B></FONT></TD>
</TR>
<TR VALIGN="TOP">
<TD WIDTH="49%"><FONT SIZE=2>&nbsp;</FONT></TD>
<TD WIDTH="3%"><FONT SIZE=2>&nbsp;</FONT></TD>
<TD WIDTH="49%"><FONT SIZE=2><B>Plan Name:<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;UNITED SECURITY BANK, N.A.<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;EMPLOYEE STOCK OWNERSHIP PLAN</B></FONT></TD>
</TR>
<TR VALIGN="TOP">
<TD WIDTH="49%"><FONT SIZE=2><B><BR>
&nbsp;</B></FONT></TD>
<TD WIDTH="3%"><FONT SIZE=2><B><BR>&nbsp;</B></FONT></TD>
<TD WIDTH="49%"><FONT SIZE=2><B><BR>
Plan Number: 001</B></FONT></TD>
</TR>
</TABLE>
<!-- end of user-specified TAGGED TABLE -->


<P><FONT SIZE=2>Dear
Applicant: </FONT></P>

<P><FONT SIZE=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;We
have made a favorable determination on your plan, identified above, based on the information supplied. Please keep this letter in your permanent records. </FONT></P>

<P><FONT SIZE=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Continued
qualification of the plan under its present form will depend on its effect in operation. (See section&nbsp;1.401-1(b)(3) of the Income Tax Regulations.) We will
review the status of the plan in operation periodically. </FONT></P>

<P><FONT SIZE=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;The
enclosed document explains the significance of this favorable determination letter, points out some features that may affect the qualified status of your employee retirement plan,
and provides information on the reporting requirements for your plan. It also describes some events that automatically nullify it. It is very important that you read the publication. </FONT></P>

<P><FONT SIZE=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;This
letter relates only to the status of your plan under the Internal Revenue Code. It is not a determination regarding the effect of other federal or local statutes. </FONT></P>

<P><FONT SIZE=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;This
determination is also subject to your adoption of the proposed amendments submitted in your letter(s) dated 2-10-95&nbsp;&amp;
10-30-95. These proposed amendments should also be adopted on or before the date prescribed by the regulations under Code Section&nbsp;401(b). </FONT></P>


<P><FONT SIZE=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;This
determination letter is applicable or the plan adopted on December&nbsp;28, 1993. </FONT></P>

<P><FONT SIZE=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;This
plan satisfies the requirements of Code section&nbsp;4975(e)(7). </FONT></P>

<P><FONT SIZE=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;This
plan has been mandatorily disaggregated, permissively aggregated, or restructured to satisfy the nondiscrimination requirements. </FONT></P>

<P><FONT SIZE=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;This
plan satisfies the nondiscrimination in amount requirement of section&nbsp;1.401(a) (4)-1(b) (2)&nbsp;of the regulations on the basis of a design-based safe harbor
described in the regulations. </FONT></P>

<P><FONT SIZE=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;This
letter is issued under Rev. Proc. 93-39 and considers the amendments required by the Tax Reform Act of 1986 except as otherwise specified in this letter. </FONT></P>

<P><FONT SIZE=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;This
plan satisfies the nondiscriminatory current availability requirements of section&nbsp;1.401(a)(4)&#151;4(b) of the regulations with respect to those benefits, rights, and
features that are currently available to all employees in the plan's coverage group. For this purpose, the plan's coverage group consists of those employees treated as currently benefitting for
purposes of demonstrating that the plan satisfies the minimum coverage requirements of section&nbsp;410(b) of the Code. </FONT></P>


<P><FONT SIZE=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;This
letter may not be relied upon with respect to whether the plan satisfies the qualification requirements as amended by the Uruguay Round Agreements Act, Pub. L. 103-465. </FONT></P>

<HR NOSHADE>
<!-- ZEQ.=2,SEQ=2,EFW="2089950",CP="UNITED SECURITY BANCSHARES",DN="2",CHK=652191,FOLIO='blank',FILE='DISK030:[02SAN2.02SAN1752]KE1752A.;7',USER='ILEONG',CD='24-SEP-2002;22:14' -->
<BR>

<P><FONT SIZE=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;The
information on the enclosed addendum is an integral part of this determination. Please be sure to read and keep it with this letter. </FONT></P>

<P><FONT SIZE=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;We
have sent a copy of this letter to your representative as indicated in the power of attorney. </FONT></P>

<P><FONT SIZE=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;If
you have questions concerning this matter, please contact the person whose name and telephone number are shown above. </FONT></P>

<!-- User-specified TAGGED TABLE -->
<TABLE WIDTH="100%" BORDER=0 CELLSPACING=0 CELLPADDING=0>
<TR VALIGN="TOP">
<TD WIDTH="49%"><FONT SIZE=2>&nbsp;</FONT></TD>
<TD WIDTH="3%"><FONT SIZE=2>&nbsp;</FONT></TD>
<TD WIDTH="49%"><FONT SIZE=2>Sincerely yours,</FONT></TD>
</TR>
<TR VALIGN="TOP">
<TD WIDTH="49%"><FONT SIZE=2><BR>
&nbsp;</FONT></TD>
<TD WIDTH="3%"><FONT SIZE=2><BR>&nbsp;</FONT></TD>
<TD WIDTH="49%"><FONT SIZE=2><BR>
/s/ Richard R. Orosco</FONT></TD>
</TR>
<TR VALIGN="TOP">
<TD WIDTH="49%"><FONT SIZE=2>&nbsp;</FONT></TD>
<TD WIDTH="3%"><FONT SIZE=2>&nbsp;</FONT></TD>
<TD WIDTH="49%"><FONT SIZE=2>Richard R. Orosco<BR>
District Director</FONT></TD>
</TR>
<TR VALIGN="BOTTOM">
<TD WIDTH="49%"><FONT SIZE=2>Enclosures:<BR>
Publication 794<BR>
Addendum</FONT></TD>
<TD WIDTH="3%"><FONT SIZE=2>&nbsp;</FONT></TD>
<TD WIDTH="49%"><FONT SIZE=2>&nbsp;</FONT></TD>
</TR>
</TABLE>
<!-- end of user-specified TAGGED TABLE -->

<HR NOSHADE>
<!-- ZEQ.=3,SEQ=3,EFW="2089950",CP="UNITED SECURITY BANCSHARES",DN="2",CHK=621290,FOLIO='blank',FILE='DISK030:[02SAN2.02SAN1752]KE1752A.;7',USER='ILEONG',CD='24-SEP-2002;22:14' -->

<P><FONT SIZE=2><B>UNITED SECURITY BANK, N.A.  </B></FONT></P>

<P><FONT SIZE=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;This plan does not provide for contributions on behalf of participants with less than one thousand hours of service during the plan year and/or does not provide
for contributions on behalf of participants not employed on the last day of the plan year. The provision(s) may, in operation, cause this plan to fail the coverage requirements of IRC 401(b) and/or
the participation requirements of IRC 401(a)(26). If this discrimination occurs, this plan will not remain qualified. </FONT></P>

<HR NOSHADE>
<!-- ZEQ.=4,SEQ=4,EFW="2089950",CP="UNITED SECURITY BANCSHARES",DN="2",CHK=190104,FOLIO='blank',FILE='DISK030:[02SAN2.02SAN1752]KE1752A.;7',USER='ILEONG',CD='24-SEP-2002;22:14' -->
<BR>
<!-- THIS IS THE END OF A COMPOSITION COMPONENT -->
<BR>
<P><br><A NAME="02SAN1752_2">QuickLinks</A><br></P><!-- TOC_BEGIN -->
<FONT SIZE=2><A HREF="#toc_ke1752_1">EXHIBIT 5.1</A></FONT><BR>
<!-- SEQ=,FILE='QUICKLINK',USER=SFLORES,SEQ=,EFW="2089950",CP="UNITED SECURITY BANCSHARES",DN="2" -->
<!-- TOCEXISTFLAG -->
</BODY>
</HTML>

</TEXT>
</DOCUMENT>
<DOCUMENT>
<TYPE>EX-23.1
<SEQUENCE>4
<FILENAME>a2089950zex-23_1.htm
<DESCRIPTION>EXHIBIT 23.1
<TEXT>
<HTML>
<HEAD>
<TITLE>
</TITLE>
</HEAD>
<BODY BGCOLOR="#FFFFFF" LINK=BLUE  VLINK=PURPLE>
<BR>
<FONT SIZE=3 ><A HREF="#02SAN1752_3">QuickLinks</A></FONT>
<font size=3> -- Click here to rapidly navigate through this document</font>
<!-- TOC_END -->
<P ALIGN="CENTER"><FONT SIZE=2><A
NAME="kg1752_exhibit_23.1"> </A>
<A NAME="toc_kg1752_1"> </A>
<BR></FONT><FONT SIZE=2><B>EXHIBIT 23.1    <BR>  </B></FONT></P>

<P ALIGN="CENTER"><FONT SIZE=2><B>MOSS ADAMS LLP<BR>
Certified Public Accountants  </B></FONT></P>

<P ALIGN="CENTER"><FONT SIZE=2><B>INDEPENDENT AUDITOR'S CONSENT  </B></FONT></P>

<P><FONT SIZE=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;We consent to the incorporation by reference in this Registration Statement on Form&nbsp;S-8 of United Security Bancshares of our report dated
January&nbsp;9, 2002 appearing in United Security Bancshares Annual Report on Form&nbsp;10-K for the year ended December&nbsp;31, 2001. </FONT></P>

<!-- User-specified TAGGED TABLE -->
<TABLE WIDTH="100%" BORDER=0 CELLSPACING=0 CELLPADDING=0>
<TR VALIGN="TOP">
<TD WIDTH="49%"><FONT SIZE=2>&nbsp;</FONT></TD>
<TD WIDTH="3%"><FONT SIZE=2>&nbsp;</FONT></TD>
<TD WIDTH="49%"><FONT SIZE=2>/s/&nbsp;&nbsp;</FONT><FONT SIZE=2>MOSS ADAMS LLP</FONT><FONT SIZE=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</FONT><HR NOSHADE></TD>
</TR>
<TR VALIGN="BOTTOM">
<TD WIDTH="49%"><BR><FONT SIZE=2><B>Stockton, California<BR>
September&nbsp;24, 2002</B></FONT></TD>
<TD WIDTH="3%"><FONT SIZE=2><B><BR>&nbsp;</B></FONT></TD>
<TD WIDTH="49%"><FONT SIZE=2><B><BR>
&nbsp;</B></FONT></TD>
</TR>
</TABLE>
<!-- end of user-specified TAGGED TABLE -->

<HR NOSHADE>
<!-- ZEQ.=1,SEQ=1,EFW="2089950",CP="UNITED SECURITY BANCSHARES",DN="3",CHK=43643,FOLIO='blank',FILE='DISK030:[02SAN2.02SAN1752]KG1752A.;8',USER='AHUTCHI',CD='25-SEP-2002;10:06' -->
<!-- THIS IS THE END OF A COMPOSITION COMPONENT -->
<BR>
<P><br><A NAME="02SAN1752_3">QuickLinks</A><br></P><!-- TOC_BEGIN -->
<FONT SIZE=2><A HREF="#toc_kg1752_1">EXHIBIT 23.1</A></FONT><BR>
<!-- SEQ=,FILE='QUICKLINK',USER=SFLORES,SEQ=,EFW="2089950",CP="UNITED SECURITY BANCSHARES",DN="3" -->
<!-- TOCEXISTFLAG -->
</BODY>
</HTML>

</TEXT>
</DOCUMENT>
</SUBMISSION>
