Nephrotoxicity is a major complication of acetaminophen (APAP), a widely used analgesic and antipyretic drug, and there is no specific treatment for APAP-induced renal damage. It has been reported that reactive oxygen metabolites or free radicals are important mediators of APAP toxicity. In this study, the protective role of melatonin (MLT) on APAP-induced nephrotoxicity was investigated in rats. For this purpose, nephrotoxicity was induced in male Wistar albino rats by intraperitoneal (i.p.) administration of a single dose of 1,000 mg/kg APAP. Some of these rats also received i.p. melatonin (10 mg/kg) 20 min after administration of APAP. The rats were sacrificed 24 h after administration of APAP. Urea and creatinine levels were measured in the blood, and levels of malondialdehyde (MDA) and glutathione (GSH), and glutathione peroxidase (GSH-Px), catalase (CAT), and superoxide dismutase (SOD) activity were determined in renal tissue. Serum urea and creatinine levels increased significantly as a result of APAP nephrotoxicity. A significant increase in MDA and decreases in GSH level and GSH-Px, CAT, and SOD activity indicated that APAP-induced renal damage was mediated through oxidative stress. Significant beneficial changes were noted in serum and tissue oxidative stress indicators in rats treated with MLT. These biochemical observations were supplemented by histopathological examination of kidney sections, which revealed that MLT also reduced the severity of APAP-induced histological alterations in the kidney. These results indicate that administration of APAP causes oxidative stress to renal tissue and that MLT protects against the oxidative damage associated with APAP.