The treatment of diabetes mellitus with excellent hypoglycemic effect that suppresses lactic acidosis without substantially increasing the blood lactate concentration. A composition for treating diabetes mellitus with hypoglycemic effect that suppresses lactic acidosis without substantially increasing the blood lactate concentration, and the composition has branched-chain amino acids and salts of biguanide derivatives and derivatives of biguanide derivatives or branched-chain amino acids as the active components. The composition will be more effective when leucine, isoleucine, or valine is included as branched-chain amino acids, and metformin as the biguanide derivative.
