Diabetes mellitus (DM) is recognized as one of the leading causes of morbidity and mortality in the world. About 5-6% of the world population suffers fromthis disease and the number of people diagnosed with diabetes is rapidly increasing. Diabetes has been demonstrated to be associated with oxidative stress and hyperglycemia, one of the most important indictors of oxidative stress. The endogenous mechanisms of enzymes and antioxidants are able to destroy the reactive species and create a balance between antioxidant and free radicals. In diabetes, the oxidative stress is increased because of the deficiency in the antioxidant defense. The intake of antioxidants, such as vitamin C, may reduce the oxidative stress associated with diabetes and hence help to restore the antioxidant defense system. The aim of this article was to investigate the effect of different doses of vitamin C on the biochemical parameters of normal and streptozotocin (STZ)-induced diabetic rats. Biochemical analysis was used to study the effect of this vitamin on the biochemical parameters of normal and diabetic rats. Liver and kidney enzymes were elevated after the onset of diabetes. Moderate doses of vitamin C significantly (P < 0.0008) reduced plasma gamma-glutamyl level in diabetic rats. Moreover, vitamin C significantly (P < 0.01) reduced the blood urea nitrogen level of diabetic rats. The plasma level of electrolytes, such as calcium and sodium, also changed significantly (P < 0.00001) after oral administration of vitamin C. Antioxidants, such as vitamin C, may ameliorate the biochemical parameters of diabetic rats.