Active center-directed inhibitors of plasmin were designed based on the structure of specific substrates of plasmin and then synthesized. Their effects on plasmin were examined and the structure-inhibitory activity relationship was studied. N^α-trans-4-Aminomethylcyclohexanecarbonyllysine 4-benzoylanilide (Tra-Lys-BZA) inhibited plasmin activities toward S-2251 and fibrin with IC₅₀ values of 15 and 6.1 μM, respectively and N^α-trans-4-aminomethylcyclohexanecarbonyllysine 4-benzylpiperidine amide (Tra-Lys-BPP) did not show any detectable inhibitory activity. Moreover, it was revealed that Tra-Lys-4-methoxycarbonylanilide inhibited plasma kallikrein more potently than plasmin.