Small molecule inhibitors of plasminogen activator inhibitor (PAI)-1 have been reported to date but their clinical effects still remain unknown. The present study was undertaken to investigate the structure–activity relationships (SAR) of newly synthesized 2-acylamino-3-thiophenecarboxylic acid dimers based upon a core structure of TM5001 (1) and TM5007 (2) that we have previously identified as orally effective PAI-1 inhibitors. In general, compounds possessing bulky or/and hydrophobic substituents (e.g. phenyl, isobutyl group) on the both thiophene rings showed potent PAI-1 inhibitory activities irrespective of the positions of the substitution. The mono-carboxyl derivative (10) exhibited PAI-1 inhibition comparable to the corresponding dicarboxyl compound (9f).