This study was done to investigate the antidiabetic effect of polygoni radix in Streptozotocin(STZ)-induced diabetic rats. Diabetes was induced by intravenous injection of STZ at a dose of 45mg/kg dissolved in citrate buffer. The ethanol extract of polygoni radix was orally administrated once a day for 7 days. The content of serum glucose, triglyceride(TG), total cholesterol were significantly decreased in polygoni radix treated STZ-sample group compared to the those of STZ-control group. The content of hepatic glycogen and activities of glucose-6-phosphate dehydrogenase(Glucose-6-PDH), glucokinase were significantly increased, but activity of glucose-6-phoshatase was decreased in polygoni radix treated STZ-sample group compared to the those of STZ-control group. These results indicated that ethanol extract of polygoni radix would have antidiabetic effect in STZ-induced diabetic rats.