Free radicals have important roles in pathogenesis of diabetes mellitus. It has been well documented that there is a link between oxidative stress and secondary complications of diabetes. In the present study we determined and evaluated changes in levels of selenium, malondialdehyde (MDA) and antioxidant vitamins (A, E, C) in serum of patients with Type II Diabetes Mellitus. Total of 200 diabetic patients (90 male, 110 female) with mean age of 54.8±11.4 years were recruited into the study. Control group was composed of 100 healthy volunteers (47 male, 53 female) with mean age of 46.4±12.3 years. In addition to aforementioned parameters, levels of fasting blood glucose, percentage HbA1C levels were determined in diabetic patients and controls. There was a significant increase in MDA level which is used as an indicator of metabolic stress. On the other hand, antioxidant vitamin (A, E, C) and selenium levels were reduced meaningfully. Reductions in Se levels were probable due to antioxidant effect of this trace element. In conclusion supplementation of antioxidant vitamins into the daily diets of diabetic patients will enhance power of non-enzymatic antioxidant defense systems.