Abstract: AIM:To investigate the effects of alpha-linolenic acid (ALA) on vascular function and oxidative stress in diabetic rats. METHODS: An experimental type 2 diabetes mellitus rat model was induced by feeding male Sprague Dawley (SD) rats a high-fat diet for 4 weeks and injecting streptozocin (STZ) i.p. at 30 mg/kg into the rats. Thirty SD rats were randomized equally into three groups: control group, diabetic group and ALA group. The rats were killed and the descending aorta was isolated 4 weeks later. Vascular function, nitric oxide (NO) production, malondialdehyde (MDA), superoxide dismutase (SOD) and catalase (CAT) were determined. RESULTS: Significant endothelial dysfunction and decreased NO production were observed in diabetic rats compared with the control group. Treatment with ALA significantly preserved endothelium-dependent vasorelaxation and increased NO production (both P<0.01 vs. diabetic group). Furthermore, treatment with ALA reduced MDA production and promoted SOD and CAT activities in the aorta compared with those in the diabetic group. CONCLUSION: These results indicate that an ALA-rich diet preserves endothelium-dependent vasorelaxation in diabetic rats, which may be related to the anti-oxidative effect of ALA.