AIM: Effects on insulin sensitivity of Die-Huang-Wan, the herbal mixture widely used to treat diabetic disorder in Chinese traditional medicine, were investigated in vivo. METHODS: The obese Zucker rats were employed as insulin-resistant animal model. Also, insulin-resistance was induced by the repeated intraperitoneal injections of long-acting human insulin at 0.5 U/kg three times daily into adult male Wistar rats. Insulin resistance was identified using the loss of tolbutamide (10 mg/kg) or electroacupuncture (EA)-induced plasma glucose lowering action. The plasma glucose concentration was examined by glucose oxidase assay. RESULTS: The plasma glucose-lowering action induced by tolbutamide was significantly enhanced in obese Zucker rats receiving the repeated administration of Die-Huang-Wan at dosage of 26 mg/kg for 3 d. Furthermore, administration of Die-Huang-Wan delayed the formation of insulin resistance in rats that were induced by the daily repeated injection of human long-acting insulin at 0.5 U/kg three times daily and identified by the loss of tolbutamide- or EA-induced hypoglycemia. In streptozotocininduced diabetic rats, oral administration of metformin at 320 mg/kg once daily made an increase of the response to exogenous short-acting human insulin 15 d later. This is consistent with the view that metformin can increase insulin sensitivity. Similar treatment with Die-Huang-Wan at an effective dose (26.0 mg/kg) also increased the plasma glucose lowering action of exogenous insulin at 10 d later. The effect of Die-Huang-Wan on insulin sensitivity seems to produce more rapidly than that of metformin. CONCLUSION: The present study found that oral administration of Die-Huang-Wan increased insulin sensitivity and delayed the development of insulin resistance in rats.