PURPOSE: Metformin is well-established oral hypoglycemic agent for adults and children with type 2 diabetes mellitus. In adults, metformin is effective as initial monotherapy with lack of weight gain. But, its beneficial role on obesity in children is less clearly defined. We assessed the effects of metformin in obese children with type 2 diabetes. METHODS: We evaluated body weight, height, body mass index, fasting blood sugar, HbA1c, lipid profiles in obese 36 children with type 2 diabetes treated with oral hypoglycemic agents at baseline, after 1 year and 2 years of treatment. We divided the subjects into three groups: metformin monotherapy, combination metformin with sulfonylurea, sulfonylurea monotherapy. The changes from baseline in three groups were measured. RESULTS: The decrease in body mass index, blood sugar & HbA1c was observed after treatment with metformin monotherapy group. Metformin monotherapy group after 1 & 2 years of treatment had a greater effect for body mass index (-1.9+/-1.7 kg/m2, -1.5+/-1.6 kg/m2, P<0.05). CONCLUSION: The Metformin monotherapy for obese children with type 2 diabetes improves glycemic control with benefits of significant improvement in body mass index.