Fifteen crude drugs used in traditional Sino-Japanese medicine were investigated to analyze their effects on fibrinolysis by plasmin. Each crude drug was extracted with water (W), boiling water(H) and hot ethanol (E). The extracts were tested for inhibitory effect on fibrinolysis by the fibrin plate method and on plasmin activity by the chromogenic substrate method, and the following results were obtained.Rhei Rhizoma, Moutan Cortex and Paeoniae Radix : Each extract showed marked inhibitory effects on fibrinolysis and plasmin activity.Atractylodis Lanceae Rhizoma : H showed an inhibitory effect on fibrinolysis.Eupolyphaga, Tabanus, Armeniacae Semen, Persicae Semen and Cnidii Rhizoma : E inhibited plasmin activity, while W and H were ineffective.One of the antiplasmin principles in Eupolyphaga (Opisthoplatia orientalis BURMEISTER) was identified as oleic acid. Some cis-unsaturated fatty acids, such as linoleic acid and palmitoleic acid, also inhibited plasmin activity.