Objectives : The purpose of this study was to determine whether the methanol extract of Cassia mimosoides var. nomame Makino, a naturally growing plant in Korea, could prevent the renal-ischemia/reperfusion injury in a rat model or not. Methods : The radical scavenging activities of the extracts, and ascorbic acid as a positive control, were measured in vitro. At one hour after an intraperitoneal injection of the extract (400 mg/kg), renal ischemia/reperfusion injury was generated by 40 min clamping of the left renal artery in rats. After renal ischemia/reperfusion and 24 hr restoration of blood circulation, the serum creatinine concentration was measured. And the extent of epithelial cell injury and apoptosis was assessed by various staining technologies. The Bax/Bcl-2 ratio and activated caspase-3 were assessed by immunohistochemistry. Results : The extract showed a slightly lower level of radical scavenging activity than that of ascorbic acid. Compared to those of the vehicle-treated group, the extract-treated group displayed a significantly smaller tubular epithelial cell injury of 54% reduction in the outer medulla region and a lower serum creatinine concentration of 50% reduction. It seems that the reduction in cellular injury is due to the attenuation of the Bax/Bcl-2 ratio, and the inhibition of caspase-3 activation by the extract of Cassia mimosoides. Conclusions : Cassia mimosoides var. nomame Makino could be a good candidate for a prophylactic agent against the ischemia/reperfusion/induced kidney injury.