Objectives : Diabetes is a disease in which the body does not produce or properly use insulin. Etiological studies of diabetes and its complications showed that oxidative stress might play a major role. Therefore, many efforts have been tried to regulate free oxygen radicals for treating diabetes and its complications. Iksujisundan has been known to be effective for the treatment of diabetes. The present study was carried out to investigate the effect of Iksujisundan on renal function, peroxynitrite(ONOO-) scavenging activity and polyol pathway in streptozotocin-induced diabetic rats. Methods : The crushed Iksujisundan was extracted 3 times, each time with 3 volumes of methyl alcohol at 60$^{circ}C$ for 24 h. The extract was filtered and evaporated under a reduced pressure using a rotary evaporator to yield 87.8g. Iksujisundan extract was orally administreted at 100 mg per 1 kg of body weight for 20 days to the diabetic rats induced by streptozotocin(60mg/kg). The effects of Iksujisundan extract on the streptozotocin-induced diabetic rats were observed by measuring the serum level of glucose, insulin, lipid components, creatinine and BUN, and also the kidney levels of superoxide anion radical(${cdot}$O2-), nitric oxide(NO) and ONOO-, and also the enzyme activities involved in the polyol pathway. Results : The effects of Iksujisundan on the streptozotocin-induced diabetic rats with regards to body weight, blood glucose and indulin levels, creatinine and BUN levels, total cholesterol and triglyceride lavels, and HDL-cholesterol levels were all shown to be good enough to prevent and cure the diabetes and its complications. Iksujisundan inhibited the generation of ${cdot}$O2-,NO and ONOO- in the kidney of streptozotocin-induced diabetic rats. Renal aldose reductase and sorbitol dehydrogenase activities were increased in the streptozotocin-induced diabetic rats were reversed toward natural activities. Conclusions : Iksujisundan might inhibit the development of diabetes and its complications by scavenging reactive oxygen and nitrogen species, thereby by reducing oxidative stresses and also by regulating the activities of polyol pathway enzymes, all of which could help to recover kidney function.