250-320g male Wistar rats were divided randomly into three groups: normal control, diabetes mellitus (DM) control and fish oil compound (FOC) treatment groups. The latter two groups were induced diabetic by streptozotocin injection. At the end of the third week after injection, the treatment group was fed FOC for 9 weeks. The results showed that FOC could decrease the plasma total cholesterol, triglycerides, low density lipoprotein-cholesterol and very low density lipoprotein cholesterol levels significantly; restrain platelet aggregation; decrease blood pressure and increase atrial natriuretic polypeptide-mRNA content. It was found that the aorta in DM rats had more serious lesions than those in the FOC group. Our study found that FOC could prevent the development of atherosclerosis in DM rats.