Type 2 diabetes mellitus is a chronic metabolic disease that seriously affects patients worldwide, and it is always among the top 10 causes of death in Taiwan. To date, still many patients who take more than three kinds of oral hypoglycemic agents could not effectively control their glycohemoglobin levels in clinics. Hypoglycemia as well as weight gain are common side effect with insulin therapy, and many patients in Taiwan are not willing to receive insulin injection. It is common for diabetic patients treated with Chinese herbal medicine in China currently, and some therapeutic effects have been published in international journals. In this study, we will evaluate whether Chinese herbal medicine, YH1, enhances the glycemic control and is safe as add-on medication in poorly controlled type 2 diabetes patients.