FIFTH AMENDMENT TO
                                CREDIT AGREEMENT


         This FIFTH AMENDMENT TO CREDIT AGREEMENT (this  "Amendment") is entered
into as of  December  17,  1999,  by and between  Smithway  Motor  Xpress,  Inc.
("Borrower"),  Smithway  Motor Xpress Corp. as Guarantor (the  "Guarantor")  and
LaSalle Bank National  Association,  formerly known as LaSalle National Bank, as
Lender (the "Lender").

                              W I T N E S S E T H:

         WHEREAS, the Borrower and the Guarantor entered into a Credit Agreement
dated as of September 3, 1997, a First Amendment to Credit Agreement dated as of
March 1, 1998,  a Second  Amendment  to Credit  Agreement  dated as of March 15,
1998, a Third Amendment to Credit  Agreement dated as of October 30, 1998, and a
Fourth Amendment to Credit  Agreement dated as of August 20, 1999  (collectively
referred to as the "Agreement"); and

         WHEREAS, the Borrower has requested certain modifications to the Agree-
ment and the Lender is willing to do so on the following terms and conditions;
and

         NOW, THEREFORE,  in consideration of the mutual agreements,  provisions
and covenants contained herein, the parties agree as follows:

         1.       Unless otherwise stated herein, all of the capitalized terms
contained in this document shall have the same meanings as contained in the
Agreement.

         2.       Section 5.14 shall be amended by inserting the following
language at the end of the Section:

         "Guarantor will deposit and maintain,  and Guarantor will cause SMSD to
         deposit and maintain,  all of its cash in commercial  deposit  accounts
         established by it at Lender."

         3.       Each of Sections 6.1, 6.2, 6.4, 6.5, 6.10, 6.11 and 6.12 of
the Agreement is amended to add at the end of such Section the following
sentence:

         "Neither  Borrower  nor  Guarantor  shall suffer or permit any of their
         respective Subsidiaries to take any action which this Section prohibits
         Borrower from taking."

         4.       Section 6.1 of the Agreement is further amended to add the
following subsection:

                  "(g)     Liens in favor of Lender."

         5.       Section 6.3 of the Agreement is amended to read in its
entirety as follows:




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                  "6.3   Investments.   Except  in  connection   with  the  SMSD
         Transactions,  neither Borrower nor Guarantor shall purchase or acquire
         or to commit to purchase  or acquire,  or suffer or permit any of their
         respective Subsidiaries to purchase or acquire or to commit to purchase
         or acquire,  any capital stock, equity interest or other securities of,
         or any interest in, any Person, or acquire substantially all the assets
         of any Person unless

                           (a)  the  cost  of  such   acquisition  or  purchase,
                  together  with  the  cost of all  other  acquisitions  made by
                  Guarantor and its Subsidiaries  during Borrower's then current
                  fiscal year, does not exceed $15,000,000; and

                           (b)      each new Subsidiary unconditionally
                  guarantees the Obligations in substantially the form attached
                  hereto as Exhibit B; and

                           (c) prior to or simultaneous with such acquisition or
                  purchase,   Guarantor   grants,   or  causes  its   applicable
                  Subsidiary  to grant,  to Lender a first  priority,  perfected
                  security  interest in the  securities  and assets  directly or
                  indirectly  acquired  in  form  and  substance  acceptable  to
                  Lender.

         6.       Section 6.9 of the Agreement is revised and amended to read in
         its entirety as follows:

                  "6.9  Indebtedness.   The  total   consolidated   Indebtedness
         (excluding  indebtedness  between  Guarantor's  consolidated  group  of
         companies  outstanding  pursuant to the SMSD Transactions) of Guarantor
         and its Subsidiaries (including Borrower) shall not exceed $75,000,000.
         Neither SMSD nor Guarantor will incur any  unconsolidated  Indebtedness
         other than Indebtedness to Lender. The indebtedness of Borrower to SMSD
         arising  pursuant  to SMSD  Transactions  shall not exceed  $32,500,000
         prior to September  30, 2000,  $35,000,000  on or after  September  30,
         2000,  but  prior  to  September  30,  2001,  $37,500,000  on or  after
         September 30, 2001, but prior to September 30, 2002.  $40,300,000 on or
         after  September  30,  2002,  but  prior to  September  30,  2003,  and
         $43,400,000 at anytime thereafter."

         7.       Section 6.10 of the Agreement shall be amended by inserting at
         the end of the Section the following language:

         "SMSD  shall  engage  in  no  business  or  activity  other  than  SMSD
         Transactions,  managing  indebtedness  within Guarantor's  consolidated
         group of companies,  and incidental  administrative  activities related
         thereto."

         8.       A new Section 6.14 shall be added to the Agreement and shall
         read in its entirety as follows:

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                  "6.14    Dividends.  Guarantor and Borrower shall not pay any
                   dividends, or permit any of their respective Subsidiaries to
                   pay any dividends or make any distributions, except

                           (a)      any Subsidiary of Guarantor may pay
                  dividends or make distributions to Borrower; and

                           (b)      dividends and distributions as part of the
                  SMSD Transactions."

         9.       A new Section 6.15 shall be added to the Agreement and shall
                  read in its entirety as follows:

                  "6.15  Disposition of Assets.  Borrower and Guarantor will not
         sell  or  otherwise  dispose  of all  or  substantially  all  of  their
         respective  assets,  rights or  properties,  and will not permit any of
         their  respective  Subsidiaries to sell or otherwise  dispose of all or
         substantially all of its assets, rights or properties."

         10.      A new Section 6.16 shall be added to the Agreement and shall
                  read in its entirety as follows:

                  "6.16    SMSD Transactions.  Borrower, SMSD and/or Guarantor
                  will not engage in any SMSD Transaction unless

                           (a)      the SMSD Transaction is in accordance with
                  applicable law;

                           (b)      SMSD, in accordance with its dividend
                  policy, promptly dividends all cash payments it receives from
                  Borrower to Guarantor;

                           (c)      Guarantor immediately loans to Borrower the
                  amount of all dividends received by Guarantor from SMSD; and

                           (d) Borrower's  initial promissory note to Guarantor,
                  and each  subsequent  note to  Guarantor,  is  evidenced  by a
                  promissory note in substantially the form of Exhibit A to this
                  Amendment."

         11.      Section 9.1 is amended to add the following new definitions:

                  ""SMSD" means SMSD Acquisition Corp., a South Dakota corpora-
         tion and wholly-owned Subsidiary of Guarantor."

                  ""SMSD  Transactions"  means  the  dividend  of  one  or  more
         promissory  notes up to the amount  permitted  under the  Agreement  to
         Guarantor  by  Borrower,  the

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          contribution  of the  notes  to  SMSD by Guarantor, the payment of
          interest on the notes to  SMSD  by  Borrower,  the  dividend  of such
          interest  payments  to Guarantor by SMSD, the lending of money in the
          amount of such dividends to Borrower by  Guarantor,  and the issuance
          of  additional  promissory notes to Guarantor by Borrower."

         12.      This Amendment will become effective upon the last to occur of
         the following events:

                  (a)      the execution and delivery of this Amendment by each
         of Borrower, Guarantor and East West;

                  (b)      the execution and delivery of a Guaranty by SMSD in
         the form of Exhibit B hereto;

                  (c)      the execution and delivery of a Security Agreement by
         SMSD in the form of Exhibit C hereto;

                  (d) the  execution  and delivery to Lender of UCC-1  financing
         statements  naming SMSD as debtor and Lender as secured party  suitable
         for filing in the office of the  Secretary of State of South Dakota and
         Iowa and otherwise in form and substance acceptable to Lender;

                  (e)      the execution and delivery to Lender of a Subordina-
         tion Agreement in the form of Exhibit D by Borrower, Guarantor and
         SMSD;

                  (f) the execution and delivery of a Secretary's Certificate of
         SMSD to Lender  certifying  the  articles  of  incorporation,  by-laws,
         authorizing board  resolutions and incumbent  officers of SMSD, in form
         and substance acceptable to Lender;

                  (g) the delivery to Lender of a good standing  certificate for
         SMSD issued by the Secretary of State of South Dakota dated not earlier
         than November 5, 1999;

                  (h)      the delivery to Lender of a legal opinion of SMSD's
         counsel substantially in the form of Exhibit E hereto;

                  (i) the delivery to Lender of a  certificate  of a Responsible
         Officer  of  Borrower  setting  forth  the  nature  and  extent  of all
         insurance  maintained  by all  Subsidiaries  of  Guarantor  pursuant to
         Section 5.6 of the Agreement and otherwise; and

                  (j) the delivery to Lender of standard  lenders'  loss payable
         endorsements  in favor of Lender on form ACCORD 27 with  respect to the
         insurance  policies  or  other  instruments  or  documents   evidencing
         insurance  coverage on the  properties of Borrower in  accordance  with
         Section  5.6  of the  Agreement  and on  the  properties  of all  other
         Subsidiaries of

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         Guarantor and endorsements to all such liability insurance policies
         naming Lender as an additional insured thereunder.

         13.  Subject  to the terms and  conditions  of this  Amendment,  Lender
consents to the SMSD  Transactions  and waives any  violations  of the Agreement
that may be caused by the  consummation of the SMSD  Transactions so long as the
SMSD Transactions are consummated expressly as set forth in this Amendment.

         14.  Borrower  shall pay 50% of the legal fees  incurred in  connection
with  the  preparation  of this  Amendment  and the  documents  and  instruments
referred to herein,  and shall pay 100% of all out of pocket  costs  incurred by
the Lender or its attorneys.

         15.  Borrower  expressly  acknowledges  and agrees that all collateral,
security  interests,  liens,  pledges,  and  mortgages  heretofore,  under  this
Amendment, or hereafter granted to Lender, including,  without limitation,  such
collateral,  security interests,  liens, pledges and mortgages granted under the
Agreement,  and all other supplements to the Agreement,  extend to and cover all
of the  obligations  of Borrower to Lender,  now existing or  hereafter  arising
including,  without limitation,  those arising in connection with the Agreement,
as amended by this Amendment,  upon the terms set forth in such agreements,  all
of which security interests,  liens, pledges, and mortgages are hereby ratified,
reaffirmed, confirmed and approved.

         16.  Borrower  represents  and  warrants  to Lender that (i) it has all
necessary  power and authority to execute and deliver this Amendment and perform
its  obligations  hereunder,  (ii) this Amendment and the Agreement,  as amended
hereby,  constitute the legal, valid and binding obligations of Borrower and are
enforceable  against  Borrower in  accordance  with their  terms,  and (iii) all
representations  and  warranties  of Borrower  contained  in the  Agreement,  as
amended,  and all other  agreements,  instruments  and other  writings  relating
thereto, are true, correct and complete as of the date hereof.

         17.  The  parties  hereto  acknowledge  and  agree  that the  terms and
provisions  of  this  Amendment  amend,  add to  and  constitute  a part  of the
Agreement.  Except  as  expressly  modified  and  amended  by the  terms of this
Amendment,  all of the other terms and conditions of the Agreement,  as amended,
and  all  documents   executed  in  connection   therewith  or  referred  to  or
incorporated  therein  remain in full force and effect and are hereby  ratified,
reaffirmed, confirmed and approved.

         18. If there is an express conflict between the terms of this Amendment
and the terms of the  Agreement,  or any of the other  agreements  or  documents
executed in connection  therewith or referred to or  incorporated  therein,  the
terms of this Amendment shall govern and control.

         19.  This Amendment may be executed in one or more counterparts, each
of which shall be deemed to be an original.


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         20. This Amendment was executed and delivered in Chicago,  Illinois and
shall be governed by and  construed in  accordance  with the  internal  laws (as
opposed to conflicts of law provisions) of the State of Illinois.

         IN WITNESS  WHEREOF,  this Fifth Amendment has been duly executed as of
the day and year specified at the beginning hereof.

                                        SMITHWAY MOTOR XPRESS, INC., as Borrower

                                        By:____/s/ G. Larry Owens_______________
                                        Title:_Executive Vice President_________

                                        Address Notice:
                                        P.O. Box 404
                                        Fort Dodge, Iowa 50501
                                        Attn: G. Larry Owens
                                        Facsimile: (515) 576-3304
                                        Tel: (515) 576-7418

                                        SMITHWAY MOTOR XPRESS CORP., as
                                        Guarantor

                                        By:____/s/ G. Larry Owens_______________
                                        Title:__Executive Vice President________

                                        Address Notice:
                                        P.O. Box 404
                                        Fort Dodge, Iowa 50501
                                        Attn: G. Larry Owens
                                        Facsimile: (515) 576-3304
                                        Tel: (515) 576-7418

                                        LASALLE BANK NATIONAL ASSOCIATION,
                                        as Lender

                                        By:____/s/ David A. Chaika______________
                                        Title:__Officer ________________________

                                        Address notices and Lending Office:
                                        135 South LaSalle Street
                                        Chicago, Illinois 60603
                                        Attn: Mr. David A. Chaika
                                        Facsimile: (312) 904-6150

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                            CONSENT AND RATIFICATION


                  The undersigned, pursuant to that certain Guaranty dated as of
September 3, 1997, is a guarantor of all of the  obligations  of the Borrower to
the Lender  under the terms of the  Agreement  and hereby  consents to the Fifth
Amendment to the Agreement. Guarantor hereby reaffirms and ratifies his guaranty
as if the same were fully set forth herein.

                                  SMITHWAY MOTOR XPRESS CORP., as Guarantor


                                  By:______/s/ G. Larry Owens___________________
                                  Title:__Executive Vice President______________



                  The undersigned, pursuant to that certain Guaranty dated as of
March 15, 1998, is a guarantor of all of the  obligations of the Borrower to the
Lender  under  the  terms of the  Agreement  and  hereby  consents  to the Fifth
Amendment to the Agreement. Guarantor hereby reaffirms and ratifies his guaranty
as if the same were fully set forth herein.

                                    EAST WEST MOTOR EXPRESS, INC., as Guarantor


                                    By:____/s/G. Larry Owens____________________
                                    Title:__Executive Vice President ___________