Background Oxidative stress has been implicated in the onset and progression of diabetes.Tongxinluo is a traditional Chinese medicine with potent antioxidant properties.The aim of this study was to test the hypothesis that pretreatment with Tongxinluo has similar effects as melatonin on preventing hyperglycemia and beta-cell damage in a rat model of streptozotocin (STZ)-induced diabetes.Methods Forty male Sprague Dawley rats were randomly assigned to four groups (n=10 each):normal control (NC)group; STZ group (70 mg/kg,i.p.); Tongxinluo (1.0 g·kg-1·d-1) pretreated (TXL+STZ) group and melatonin (200μg·kg-1·d-1) pretreated (MLT+STZ) group.Tongxinluo and melatonin were administered by gavage beginning 8 days before STZ injection and continuing until the end of the study (15 days after STZ administration).Blood glucose levels and body weights, malondialdehyde (MDA),and reduced glutathione (GSH) levels were measured,and immunofluorescence studies were performed in all of the groups.Results Pretreatment with Tongxinluo,as with melatonin,attenuated severe hyperglycemia and weight loss induced by STZ.In pancreatic homogenates,MDA levels were significantly lower and GSH levels were significantly higher in Tongxinluo pretreated group and in melatonin pretreated group than those in STZ group.Values of insulin staining were significantly improved in Tongxinluo pretreated group and in melatonin pretreated group as compared with those in STZ group.Conclusions Tongxinluo,as melatonin,prevented hyperglycemia and beta-cell destruction induced by STZ in rats through reducing oxidative stress in pancreatic tissues.Tongxinluo may provide an altative therapy for the prevention and treatment of diabetes.