Oxygen free radicals are important components involved in pathophysiological tissue alteration observed during ischemia/reperfusion (I/R). This study was designed to determine the possible protective effect of aqueous garlic extract (AGE) on renal I/R injury. Wistar albino rats were unilaterally nephrectomized and subjected to 45 minutes of renal pedicle occlusion followed by 6 hours of reperfusion. AGE (I mL/kg, i.p., corresponding to 500 mg/kg) or vehicle was administered twice: 15 minutes prior to ischemia and immediately before the reperfusion period. At the end of the reperfusion period, rats were killed by decapitation. Kidney samples were taken for histological examination or determination of levels of free radicals; renal malondialdehyde (MDA), an end product of lipid peroxidation; glutathione (GSH), a key antioxidant; and myeloperoxidase (MPO) activity, an index of tissue neutrophil infiltration. Renal tissue collagen content, as a fibrosis marker, was also determined. Creatinme and urea concentrations in blood were measured for the evaluation of renal function. The results revealed that I/R-induced nephrotoxicity, as evidenced by increases in blood urea and creatinine levels, was reversed by AGE treatment. The levels of free radicals, as assessed by the nitro blue tetrazolium test, were increased. Moreover, the decrease in GSH levels and the increases in MDA levels and MPO activity induced by I/R indicated that renal injury involves free radical formation. Treatment of rats with AGE (1 mL/kg) restored the reduced GSH levels, while it decreased free levels of radicals and MDA as well as MPO activity. Collagen contents of the kidney tissues increased by I/R were reversed back to the control levels with AGE. Since AGE administration reversed these oxidant responses and improved renal function and damage at the microscopic level, it seems likely that AGE protects kidney tissue against I/R-induced oxidative damage.