Antithrombotic activities, namely, in vitro platelet aggregation and in vivo pulmonary thrombosis, of the methanolic extract of aged vinegar were evaluated. The ability of the extract to inhibit platelet aggregation induced by adenosine diphosphate (ADP) and thrombin was concentration-dependent. IC(50) values for the inhibition of platelet aggregation induced by ADP and thrombin were 1.7 +/- 0.3 and 8.9 +/- 1.9 mg/mL, respectively. When administered orally at >100 mg/kg of body weight, the extract protected the rats against thrombotic death induced by collagen and epinephrine. Furthermore, the low molecular weight fraction of the extract showed strong fibrinolytic activity and altered coagulation parameters such as activated partial thromboplastin time (APTT), prothrombin time (PT), and throbin time (TT) in rat platelet. These results suggested that the antithrombotic ability of the vinegar extract corresponded to both antiplatelet and anticoagulation activities.