This study was carried to investigate the antidiabetic metabolism effect of water extract $Cordyceps$ $Militalis$(C.M.) in Streptozotocin(STZ) induced diabetic rats. Diabetes were induced by intravenous injection of STZ at a dose of 42mg/kg,b.w. dissolved in citrate buffer. The water extract of C.M. was orally administrated once a day for 7 days at a dose of 500mg/kg,b.w(body weight). or 1,000mg/kg.b.w. The content serum glucose was significantly decreased in C.M. treated group compared to the those of STZ-control group. The content of hepatic glycogen and activities of glucose-6-phosphate dehydrogenase(G-6-PDH), glucokinase(GK) were significantly increased, but activity of glucose-6-phoshatase(G-6-Pase) was significantly decreased in C.M. treated group compared to the those of STZ-control group. These results indicated that water extract of C.M. would have antidiabetic metabolism effect in STZ-induced diabetic rats.