Objectives : Diabetes is a disease in which the body does not produce or properly use insulin. Etiological studies of diabetes and its complications have shown that oxidative stress might play a major role. Therefore, many methods have been tried to regulate free oxygen radicals for treating diabetes and its complications. Ojung-hwan, composed of five crude herbs, has been considered effective for treating symptoms of aging. In male ob/ob mouse of severe obesity, hyperinsulinemia and hyperlipidemia, which are features of NIDDM, the hyperglycemic activities and mechanisms of Ojung-hwan were examined. Methods : Mice were grouped and treated for 5 weeks as follows. Both the lean (C57/BL6J black mice) and diabetic (ob/ob mice) control groups received standard chow. The experimental groups were fed a diet of chow supplemented with 30 and 90 mg Ojung-hwan per 1 kg of body weight for 14 days. The effects of Ojung-hwan extract on the ob/ob mice were observed by measuring the serum levels of glucose, insulin, lipid components, and the kidney levels of superoxide anion radical (${cdot};O{_2}{^-}$), MDA+HAE, GSH/GSSG ratio, and also the enzyme activities involved in polyol pathway. Results : Ojung-hwan lowered the levels of serum glucose and insulin in a dose-dependent manner. Total cholesterol, triglyceride and free fatty acid levels decreased, while the HDL-cholesterol level increased, in Ojung-hwan treated groups. Renal aldose reductase and sorbitol dehydrogenase activities increased in the ob/ob mice, whereas they were inhibited in the Ojung-hwan treated groups. Ojung-hwan inhibited the generation of ${cdot};O{_2}{^-}$ in the kidney. Finally, MDA+HAE levels increased and GSH/GSSG ratio decreased in the ob/ob mice, whereas they improved in the Ojung-hwan treated groups. Conclusions : Ojung-hwan showed antidiabetic and antihyperlipidemic activities by regulating theactivities of polyol pathway enzymes, scavenging reactive oxygen species and reducing the MDA+HAE levels in the ob/ob mice.