Objectives : This study aimed at investigating whether aqueous extract of Radix et Rhizoma Rhei (AR) ameliorates renal and vascular complications in diabetic rats. Methods : The experiment operated for 6 weeks. The rats were divided into 4 groups: normal group, diabetic group (control group), diabetic group treated with AR (100 mg/kg/day) for the last 3 weeks, and diabetic group treated with AR (200 mg/kg/day) for the last 3 weeks. Results : There were no significant changes in the renal functional parameters by treatment of AR in the diabetic rats. Aorta segment in the diabetic rats revealed a thickening of intima and media, which was ameliorated by treatment with AR. The aortic expression level of endothelin-1 was also significantly attenuated by treatment with AR. Conclusions : Treatment with AR could not ameliorate renal functional defects, but improved vascular complication in diabetic rats.