Objectives : The object of this study was to observe the effects of Gamioryung-san (GOS), which consists of 22 types of herbs, on streptozotocin (STZ)-induced diabetic nephropathy rats. Methods : Three different dosages of GOS were orally administered once a day for 28 days from 3 weeks after STZ treatment. Six groups, each of 8 rats per group were used. Changes on the body weights, blood glucose levels, serum BUN and creatinine levels, urine volumes, and UAER were observed with changes on the kidney malondialdehyde contents and glutathione, dismutase and catalase contents. In addition, histopathology of kidney, pancreas, thymus and spleen were observed. The results were compared with antioxidant silymarin 100 mg/kg, of which the effects on STZ -induced diabetes and related complications are already confirmed. Results : As a result of treatment of GOS 800, 400 or 200 mg/kg for 28 days, STZ-induced decreases of body weights, hyperglycemia, atrophic changes of pancreatic islets with decreases of insulin-immunoreactive cells and decreases of glucagon -immunoreactive cells were inhibited dose-dependently. Increases in kidney weight, serum BUN and creatinine levels, urine volumes, UAER, vasodilated atrophic glomerulus and abnormal tubules were inhibited dose-dependently. Also increases of kidney MDA contents and decreases of GSH contents, SOD and CAT activities, decreases of thymus and spleen weights, and atrophic changes at histopathological observation were also inhibited. The effects of GOS 400 mg/kg showed similar effects to silymarin 100 mg/kg. Conclusions : These results suggest that 400 mg/kg of GOS retarded the STZ-induced diabetic nephropathies as similarly to silymarin 100 mg/kg, through modulations of oxidative stress and immune systems.