The possibility of Chungpesagantang, Sunghyangjunggisan and Yangkyuksanwhatang, which have been recommended for stroke patients with constipation in traditional Korean clinics, was evaluated as a novel antithrombotic agent. Chungpesagantang potently inhibited ADP- and collagen-induced rat platelet aggregation in vitro, but Sunghyangjunggisan and Yangkyuksanwhatang did not inhibit it. However, all tested herbal formulae inhibited in vivo ADP- and collagen-induced rat platelet aggregation and extended the bleeding time of mice tails. All these herbal formulae did not affect certain plasma clotting times such as APTT, PT and TT. Among these herbal formulae, Chungpesagantang showed significant protection against death due to pulmonary thrombosis in mice. Based on these findings, these herbal formulae should prevent thrombosis and cardiovascular diseases such as myocardial infraction stroke, and arteriosclerosis.