Gentamicin (GM) is an antibiotic whose clinical use is limited by its nephrotoxicity. Experimental evidences suggest a role of reactive oxygen species in GM-induced nephrotoxicity. Therefore, we investigated if aged garlic extract (AGE), an antioxidant, has a protective role in this experimental model. Four groups of male Wistar rats were studied: 1) Control (CT), injected subcutaneously (s.c.) and intraperitoneally (i.p.) with saline, 2) GM, treated s.c. with GM (70 mg/kg/12 hours/4 days), 3) AGE, treated i.p with AGE (1.2 mL/kg/12 hours/6 days), and 4) GM + AGE treated with GM and AGE. The treatment with AGE started two days before the first dose of GM (GM + AGE group) or saline (AGE group). Animals were sacrificed on day 5, and blood, urine, and kidneys were obtained. Nephrotoxicity was made evident by: 1) the increase in blood urea nitrogen and plasma creatinine, 2) the decrease in plasma glutathione peroxidase (GPx) activity and the urinary increase in N-acetyl-beta-D-glucosaminidase activity and total protein, and 3) necrosis of proximal tubular cells. These alterations were prevented or ameliorated by AGE treatment. Furthermore, AGE prevented the GM-induced increase in the renal levels of oxidative stress markers: nitrotyrosine and protein carbonyl groups and the decrease in manganese superoxide dismutase (Mn-SOD), GPx, and glutathione reductase (GR) activities. The protective effect of AGE was associated with the decrease in the oxidative stress and the preservation of Mn-SOD, GPx, and GR activities in renal cortex. These data suggest that AGE may be a useful agent for the prevention of GM-nephrotoxicity.