In this article we report the effects of low and high fat diets on the arterial thrombosis tendency in rats. The animal system used was the aorta loop model, in which we compared the effect of saturated (hardened coconut oil, HCO) and unsaturated (sunflower seed oil, SSO; corn oil, CO) fatty acids on the arterial thrombosis tendency at high fat intake (50 energy%, 45 energy% of which was either HCO, SSO, or CO). Under these conditions both SSO and CO had a beneficial effect (relative to HCO) on the arterial thrombosis tendency. In a subsequent study we compared these high fat diets with a low fat diet (5 energy%). As compared with the low fat diet, only CO significantly decreased the thrombosis risk. Serum vitamin K and triglycerides had decreased substantially after the CO diet, and to a much lesser extent after the SSO diet. It is concluded that corn oil may have a mildly anticoagulant effect, the potential benefit of which is discussed.