Platelet anti-aggregating activities were tested with analogs of protocatechuic acid and gallic acid. Six of them which showed comparable inhibitory effects with aspirin against collagen induced platelet aggregation were selected and their anti-thrombotic effects were evaluated in the mouse thrombosis model and compared with those of aspirin and paeonol. At the dose of 50 mg/kg, p.o., ethyl gailate(13) treated group showed higher % of recovery within 6 min of thrombotic challenge and lower mortality within 5 min than aspirin treated group.