This study investigated the effect of Corni Fructus(Cornus officinalis Sieb. et Zucc.) extract on hyperglycemia and renal function in streptozotocin-induced diabetic rats. Male Sprague-Dawley rats were divided into three groups including normal control(NC), diabetic control(DC), and diabetic treatment with Corni Fructus(DCF). Over a 4-week experimental period, Corni Fructus aqueous extract was administered orally at 500 mg/kg BW/day. The final fasting serum glucose, serum urea nitrogen, triglyceride, urinary total protein level, and relative weight of the left kidney in the DCF group were significantly lower than the DC group. Serum insulin level in the DCF group was higher than the DC group by 23%. The renal xanthine oxidase and superoxide dismutase activities in the DCF group were significantly lower than the DC group. The renal catalase activity in the DCF group was significantly higher than the DC group. In conclusion, these results indicated that Corni Fructus can reduce glucose level and prevent or retard the development of diabetic complication via its antioxidative effect and protecting against diabetic renal damage in streptozotocin-induced diabetic rats.