Oxidative stress is currently suggested to play as a pathogenesis in the development of diabetes mellitus. The present study was designed to evaluate the effect of Casearia esculenta root extract on oxidative stress-related parameters in streptozotocin (STZ) -induced diabetic rats. Antidiabetic treatment with C. esculenta root extract (45 days) significantly (p < .05) decreased thiobarbituric acid reactive substances (TBARS) and remarkably improved tissue antioxidants status such as glutathione (GSH), ascorbic acid (vitamin C) and alpha-tocopherol (vitamin E) in liver and kidney of STZ-diabetic rats. In diabetics rats, the activities of enzymatic antioxidants such as superoxide dismutase (SOD, EC 1.11.1.1) catalase (CAT, EC 1.11.1.6) were decreased significantly while the activity of glutathione peroxidase (GPx, EC 1.11.1.9) decreased in the liver and increased in the kidney. The treatment of diabetic rats with C. esculenta root extract over a 45-day period returned these levels close to normal. These results suggest that C. esculenta root extracts exhibit antiperoxidative as well as antioxidant effects in STZ-induced diabetic rats.