SIXTH AMENDMENT TO
                                CREDIT AGREEMENT


     This SIXTH AMENDMENT TO CREDIT AGREEMENT (this "Amendment") is entered into
as of July 1, 2000, 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, a
Fourth  Amendment  to Credit  Agreement  dated as of August 20, 1999 and a Fifth
Amendment  to Credit  Agreement  dated as of  December  17,  1999  (collectively
referred to as the "Agreement"); and

     WHEREAS, the Borrower has requested certain  modifications to the Agreement
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  6.13 of the  Agreement is deleted in its entirety as of June 1,
2000 and is replaced with the following:

                         Section 6.13 Debt Service  Coverage  Ratio. As measured
                    on the last day of each  fiscal  quarter  hereafter  for the
                    twelve  month period then  ending,  the  Borrower  shall not
                    permit  the ratio of (I) EBITDA  less (a) all  income  taxes
                    actually  paid  during  such  period,  less  (b)  20% of its
                    Capital Expenditures incurred during such period to (II) the
                    Current  Maturities  of  Indebtedness,   plus  (a)  interest
                    expense of Guarantor and its  Subsidiaries on a consolidated
                    basis for such period,  determined in accordance  with GAAP,
                    deducted  from  Consolidated  Net  Income (or Loss) for such
                    period,  plus  (b)  33% of the  sum of (i)  the  outstanding
                    principal balance on the Revolving Loan plus any outstanding
                    Letters of Credit,  less (ii) 85% of the aggregate amount of
                    the Borrower's then existing Eligible  Accounts,  to be less
                    than 1.0:1.0.

     3. There is hereby added to the Agreement the following Section 6.17:

                         Section  6.17 Minimum Net Profit.  The  Borrower  shall
                    have  after  tax  earnings  at the end of each  fiscal  year
                    hereafter of not less than $1.00.

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

     "Capital Expenditures" shall mean, for any period,  expenditures (including
the aggregate amount of expenditures under Capital Leases) made by the Guarantor
or its  Subsidiaries to acquire or construct  fixed assets,  plant and equipment
(including renewals, improvements and replacements, but excluding repairs unless
such repairs are required to be capitalized in accordance with GAAP) during such
period  computed in accordance  with GAAP;  provided  that Capital  Expenditures
shall not include expenditures made with the insurance proceeds or sale proceeds
for fixed assets, plant and equipment.

     "Capital  Lease"  shall  mean a lease  with  respect to which the lessee is
required  concurrently  to  recognize  the  acquisition  of  an  asset  and  the
incurrence of a liability in accordance with GAAP.


<PAGE>

     "Current  Maturities  of  Indebtedness"  shall  mean at any  time  and with
respect  to  any  item  of  Indebtedness,   the  portion  of  such  Indebtedness
outstanding at such time which by the terms of such Indebtedness or the terms of
any instrument or agreement relating thereto is due on demand or within one year
from  the  time of  determination  (whether  by  sinking  fund,  other  required
prepayment  or final  payment at  maturity)  and is not  directly or  indirectly
renewable,  extendible  or  refundable  at the  option of the  obligor  under an
agreement or firm  commitment  in effect at such time to a date one year or more
from such time.

     5. This Amendment will become  effective upon the execution and delivery of
this Amendment by each of Borrower, Guarantor, East West and SMSD.

     6. 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.

     7. 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.

     8. 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.

     9. 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.

     10. 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.

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

     12. 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.

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<PAGE>

         IN WITNESS WHEREOF, this Sixth 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:  Exec. V.P.

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

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<PAGE>


                                   SMITHWAY MOTOR XPRESS CORP., as Guarantor

                                   By:  /s/ G. Larry Owens
                                   Title:  Exec. V.P.

                                   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:  AVP

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

                            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 Sixth  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:  Exec. V.P.


     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  Agreementand  hereby  consents to the Sixth 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:  Exec. V.P.

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<PAGE>

     The undersigned, pursuant to that certain Guaranty dated as of December 17,
1999,  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 Sixth  Amendment to
the Agreement.  Guarantor  hereby  reaffirms and ratifies his guaranty as if the
same were fully set forth herein.

                                   SMSD ACQUISITION CORP., a South Dakota
                                   corporation, as Guarantor


                                   By:  /s/ G. Larry Owens
                                   Title:  Exec. V.P.

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