Secondary failure of sulfonylureas (SUs) can occur in about 30%-40% of type 2 diabetic patients after treatment with SUs for 5 years, although SUs are widely used in type 2 diabetic patients. This study was designed to evaluate the effectiveness and safety of adding compound preparation of pioglitazone and metformin for type 2 diabetic patients who have bad glycemic control with the initial treatment of SUs.