Abstract: Objective To explore the role of oxidative stress on the initiation and developmentof the diabeticmyopathy of rats.Methods Diabetic rats were induced by injection of streptozotocin (STZ) into the tail vein.The malondialdehyde (MDA)level and the total superoxide dismutase (SOD)activity in the quadriceps femoris were measured at the time of 1 month,3 months and 6 months of experin ental diabetes.The pathological changes of diabetic rats were exam fined by light microscopy.Results The MDA level increased significantly in the diabetic group as compared to control group at all time intervals(1.81±0.30 vs 0.96±0.35,P<0.01,1.14±0.20 vs 0.91±0.21,P<0.05,1.32±0.29 vs 0.97±0.22,P<0.05).The total SOD activity increased significantly in the diabetic group as compared to control group at lmonth (47.43±6.23 vs 34.21±4.04,P<0.001),and dropped to baseline at 3 month,while decreased significantly at 6 month (26.10±5.89 vs 32 67±5.56 P<0.05).Inspection of the quadriceps femoris by lightmicroscopy demonstrated that the diabetic rats exhibited pathological changes at 3 month and the changes were more serious as the diabetic duration extended.Conclusion Oxidative stress was found to occur before the initiation of diabetic myopathy and was maintained in the developing of the diabeticmyopathy This implies that the oxidative stress plays an important role in the initiation and developmentof the diabetic myopathy.