Diabetes mellitus is a metabolic disease associated with multiple organ damage, dysfunction and failure. Metformin is widely used to treat diabetes, but regular exercise also improves metabolic control in diabetic individuals and has an important role in the management of this disease. In this work, we compared the effects of metformin and physical training in diabetic male Wistar rats. Four groups of rats were used: (n=6 per group): sedentary control (SC), sedentary diabetic (SD), trained diabetic (DT) and metformin diabetic (MD). Diabetes was induced with alloxan (30 mg/kg, b.w.). The physical training protocol consisted of a 1 h swimming session/day, five days/week for eight weeks with a load corresponding to 5% of the body weight. Metformin treatment consisted in 1.4 mg/ml per day, administered in the drinking water. At the end of the experimental period, the rats were sacrificed and blood was collected to measure serum glucose, insulin and albumin. Glycogen was quantified in gastrocnemius muscle, liver and heart, the protein/DNA ratio was mensured in liver and heart triglycerides was also measured in the heart. Diabetes reduced the serum insulin and liver glycogen levels and the protein/DNA ratio, but increased the serum glucose and heart glycogen levels; there were no significant variations in serum albumin levels. Physical training increased the muscle glycogen level. Physical training and metformin were equally effective in reducing the serum glucose concentration and in restoring the hepatic and cardiac glycogen stores and the hepatic protein/DNA ratio in diabetic rats. These results show that chronic exercise was as effective as metformin in improving the metabolic profile of diabetic rats and in preventing diabetes-induced alterations.