Exhibit 8

                 [WILLIAMS, MULLEN, CLARK & DOBBINS LETTERHEAD]



                                  July __, 1999


Board of Directors
Southern Financial Bancorp, Inc.
37 E. Main Street
Warrenton, Virginia 22186

Board of Directors
The Horizon Bank of Virginia
140 Park Street, SE
Vienna, Virginia  22180

         Re:   Tax Opinion - Merger of The Horizon Bank of Virginia
               with  and  into  Southern   Financial   Bank  a  wholly  owned
               subsidiary of Southern Financial Bancorp, Inc.

Ladies and Gentlemen:

         You have  requested  our  opinion  as to  certain  federal  income  tax
consequences  of the  proposed  merger (the  "Merger")  of The  Horizon  Bank of
Virginia  ("HBV") with and into Southern  Financial  Bank  ("Surviving  Bank") a
wholly owned subsidiary of Southern Financial Bancorp,  Inc. ("SFB") pursuant to
the  Agreement  and Plan of  Reorganization,  dated May 3, 1999,  between  these
parties.  Our opinion is given  pursuant to Section  6.1(d) of the Agreement and
Plan of Reorganization.

                                     FACTS:

         HBV is a corporation and state bank organized under Virginia law. HBV's
principal executive offices are located at 140 Park Street, SE, Vienna, Virginia
22180.

         SFB is a Virginia corporation and registered bank holding company under
the Bank Holding Company Act of 1956, as amended. Surviving Bank, a wholly owned
subsidiary of SFB, is a corporation and state bank organized under Virginia law.
SFB's  principal  executive  office is located at 37 E. Main Street,  Warrenton,
Virginia 22186

         Pursuant  to the  Agreement  and  Plan of  Reorganization,  HBV will be
merged with and into Surviving  Bank in accordance  with the provisions of Title
13.1 of the Code of Virginia



of  1950,  as  amended.   Each  outstanding  share  of  HBV  common  stock  will
automatically become and be converted into 0.63 shares of SFB common stock. Cash
will be paid in lieu of fractional shares. After the Merger, Surviving Bank will
continue its existing  business and  operations as a wholly owned  subsidiary of
SFB.

         In connection with this opinion, we have reviewed (i) the Agreement and
Plan of  Reorganization,  (ii) SFB's  Registration  Statement on Form S-4, dated
July __, 1999,  including the  Prospectus  and Joint Proxy  Statement  contained
therein,  and (iii) such other documents concerning the Merger as we have deemed
necessary ((i),  (ii), and (iii)  collectively,  the "Merger  Documents").  With
respect to the various factual matters material to our opinions,  we have relied
upon  certificates  of  certain  officers  of and HBV and  SFB  (the  "Officers'
Certificates"). We have assumed the correctness of the factual matters contained
in such  reliance  sources and have made no  independent  investigation  for the
purpose of confirming that such factual  matters are correct.  As to all matters
in which a person or entity has represented that such person or entity either is
not a party to,  does not  have,  or is not  aware  of,  any plan or  intention,
understanding  or  agreement,  we have  assumed  that  there is in fact no plan,
intention, understanding or agreement. We have also assumed that the Merger will
be consummated in accordance with the Agreement and Plan of Reorganization.

         We have assumed (i) the  genuineness  of all  signatures  on the Merger
Documents, (ii) the due authorization,  execution, and delivery of all documents
and the validity  and binding  effect  thereof,  (iii) the  authenticity  of all
documents submitted to us as originals,  (iv) the conformity to the originals of
all documents  submitted to us as copies and the  authenticity  of the originals
from which the copies were made, and (v) the legal capacity of natural persons.

                                    OPINION:

         Based  on  the   foregoing   and   subject  to  the   limitations   and
qualifications set forth herein, we give our opinion as follows:

1.       The Merger  will  qualify  as a  reorganization  within the  meaning of
Sections  368(a)(1)(A)  and  368(a)(2)(D)  of the  Internal  Revenue  Code  (the
"Code"),  and HBV and SFB will each  qualify  as a "party  to a  reorganization"
within the meaning of Section 368 (b) of the Code.

2.       No gain or loss will be  recognized  for federal tax purposes by HBV or
SFB as a result of the Merger.



3.       No gain or loss will be  recognized  for  federal  tax  purposes by the
shareholders of HBV as a result of the exchange of their common stock solely for
the common stock of SFB.

4.       Any shareholder of HBV who receives cash in lieu of a fractional  share
interest  shall  be  treated  as  receiving  a  payment  in  redemption  of such
fractional  interest  subject to the provisions of Section 302 of the Code. Gain
or loss will be realized  and  recognized  to such  shareholder  measured by the
difference  between the  redemption  price and the portion of the  shareholder's
basis in HBV stock allocable to such fractional share interest.

5.       The  aggregate  tax basis of the shares of SFB stock  received  by each
shareholder   of  HBV  will  be  equal  to  the  aggregate  tax  basis  of  such
shareholder's shares of HBV stock surrendered therefor in the Merger.

6.       The holding period under Section 1223 of the Code for the shares of SFB
stock  received by each  shareholder  of HBV will include the holding period for
the shares of HBV stock of such shareholder  surrendered therefor in the Merger,
provided that the HBV shareholder held such stock as a capital asset on the date
of the Merger.

         In rendering our opinion, we have considered the applicable  provisions
of the Code, Treasury  Regulations  promulgated  thereunder,  pertinent judicial
authorities,  interpretive  rulings of the Internal Revenue  Service,  and other
authorities  as we have  considered  relevant.  Our  opinion  is  limited to the
federal tax law of the United  States of America and is expressed as of the date
hereof.  We do not assume any  obligation to update or supplement our opinion to
reflect any fact or  circumstance  which hereafter comes to our attention or any
change in law which  hereafter  occurs.  Our opinions are limited to the matters
expressly stated; no opinion is implied or may be inferred beyond such matters.

         Our opinion  expressed herein is made in connection with the Merger and
is solely for the benefit of HBV, SFB and its shareholders. We hereby consent to
the filing of this opinion as an exhibit to the  Registration  Statement,  which
has been filed by SFB with the  Securities and Exchange  Commission,  and to the
reference  to  our  firm  under  the  caption   "Certain   Federal   Income  Tax
Consequences"  in the  Prospectus  and  Proxy  Statement  forming  a part of the
Registration Statement. This opinion may not, without our prior written consent,
be  otherwise  distributed  or relied upon by any other  person,  filed with any
other government agency or quoted in any other document.



                                      Very truly yours,

                                      WILLIAMS, MULLEN, CLARK & DOBBINS



                                      By:______________________________