Male rats were fed diets containing perilla oil, sardine oil or corn oil for 15 weeks in order to investigate their antithrombotic effects. Rats given perilla oil and sardine oil diets showed significantly longer bleeding time, and lower level of malondialdehyde generation during thrombin-induced aggregation of platelets than rats given corn oil. With regard to the composition of platelet fatty acid, the ratio of eicosapentaenoic acid(EPA) $(20:5{omega}3)$ to arachidonic acid $(20:4{omega}6)$ of perilla oil, sardine oil and corn oil treated rats were 0.54, 0.96 and 0.01, respectively, suggesting that linolenic acid $(18:3{omega}3)$ of perilla oil was metabolized to EPA which is known to have antithrombotic activity.