We compared the effects of different n-3 polyunsaturated fatty acids (PUFA) on platelet aggregation and lipid metabolism in rats. alpha-Linolenic acid (ALA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) were used as n-3 PUFA sources. The rats were fed diets containing 10% lipids (polyunsaturated/saturated fatty acid (P/S) ratio = 1.0; n-3/n-6 = 0.02 for the control group, 0.2 for the test groups) for two weeks. The platelet counts, platelet aggregation, and production of thromboxane A2 (TXA2), plasma total cholesterol (TC) and triacylglycerols (TG) were not different between the ALA group and the control group, but showed a decreasing tendency for the EPA group and significant decreases for the DHA group. The production of prostacyclin in the aorta was significantly decreased in all of the n-3 PUFA groups when compared with that in the control group. Liver TC and TG concentrations were significantly decreased in the DHA group when compared with those in the control group. Based on the above, it is assumed that the physiological action exerted by n-3 PUFA differs by type and that DHA is a more effective n-3 PUFA, both for suppressing platelet aggregation and for modulating lipid metabolism in the plasma and liver of rats.