The protective action against oxidative stress of red cabbage (Brassica oleracea) extract was investigated. Diabetes was induced in male Wistar rats using streptozotocin (60 mg/kg body weight). Throughout the experimental period (60 days), diabetic rats exhibited many symptoms including loss of body weight, hyperglycemia, polyuria, polydipsia, renal enlargement and renal dysfunction. Significant increase in malondialdehyde, a lipid peroxidation marker, was observed in diabetic kidney. This was accompanied by a significant increase in reduced glutathione and superoxide dismutase activity and a decrease in catalase activity and in the total antioxidant capacity of the kidneys. Daily oral ingestion (1 g/kg body weight) of B. oleracea extract for 60 days reversed the adverse effect of diabetes in rats. B. oleracea extract lowered blood glucose levels and restored renal function and body weight loss. In addition, B. oleracea extract attenuated the adverse effect of diabetes on malondialdehyde, glutathione and superoxide dismutase activity as well as catalase activity and total antioxidant capacity of diabetic kidneys. In conclusion, the antioxidant and antihyperglycemic properties of B. oleracea extract may offer a potential therapeutic source for the treatment of diabetes.