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No UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington , D.C. 20549 FORM 10 - K ANNUAL REPORT PURSUANT TO SECTION 13 0R 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 OR TRANSITION REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 Delaware ( State of incorporation ) For the fiscal year ended December 31 , 2020 Commission file number 0-15010 MARTEN TRANSPORT , LTD . ( Exact name of registrant as specified in its charter ) 129 Marten Street Mondovi , Wisconsin ( Address of principal executive offices ) Title of each class : COMMON STOCK , PAR VALUE $ .01 PER SHARE 54755 ( Zip Code ) Securities registered pursuant to Section 12 ( b ) of the Act : Trading symbol : MRTN ( I.R.S. Employer Identification no . ) Securities registered pursuant to Section 12 ( g ) of the Act : NONE ( 715 ) 926-4216 ( Registrant's telephone number ) 39-1140809 Accelerated filer Name of each exchange on which registered : THE NASDAQ STOCK MARKET LLC ( NASDAQ GLOBAL SELECT MARKET ) Indicate by check mark if the Registrant is a well - known seasoned issuer , as defined in Rule 405 of the Securities Act . Yes Non - accelerated filer Indicate by check mark if the Registrant is not required to file reports pursuant to Section 13 or 15 ( d ) of the Exchange Act . Yes No X Indicate by check mark whether the Registrant ( 1 ) has filed all reports required to be filed by Section 13 or 15 ( d ) of the Securities Exchange Act of 1934 during the preceding 12 months ( or for such shorter period that the Registrant was required to file such reports ) , and ( 2 ) has been subject to such filing requirements for the past 90 days . Yes > No Indicate by check mark whether the Registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S - T ( Section 232.405 of this chapter ) during the preceding 12 months ( or for such shorter period that the Registrant was required to submit such files ) . Yes > No Indicate by check mark whether the Registrant is a large accelerated filer , an accelerated filer , a non - accelerated filer , a smaller reporting company , or an emerging growth company . See the definitions of " large accelerated filer , " " accelerated filer , ” " smaller reporting company , " and " emerging growth company " in Rule 12b - 2 of the Exchange Act . Large accelerated filer Smaller reporting company Emerging growth company If an emerging growth company , indicate by check mark if the Registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13 ( a ) of the Exchange Act . □ Indicate by check mark whether the Registrant has filed a report on and attestation to its management's assessment of the effectiveness of its internal control over financial reporting under Section 404 ( b ) of the Sarbanes - Oxley Act ( 15 U.S.C. 7262 ( b ) ) by the registered public accounting firm that prepared or issued its audit report . Î Indicate by check mark whether the Registrant is a shell company ( as defined in Exchange Act Rule 12b - 2 ) . Yes □ No ²