The present study was undertaken to elucidate the hypoglycemic effect and inhibitory effect of Cudrania tricuspidata root bark on aldose reductase activity. C. tricuspidata MeOH ext. 1,000 mg/kg showed a significant blood glucose lowering effect on alloxan-induced hyperglycemic rats and increasing body weight. C. tricuspidata MeOH ext. showed a potent inhibitory effect on bovine lens aldose reductase.