Allium cepa (Common Onion), one of the most widely grown crops in world, is believed to possess medicinal potency. The present study was designed to investigate the effect of Allium cepa (ACE) administration on oxidative stress-mediated hepatotoxicity following aluminum chloride (AlCl3) administration. 24 adult male wistar rats weighing 175 g were randomly divided into vehicle-treated (control), ACE, aluminum chloride (AlCl3) and ACE+AlCl3 groups. Rats were given single oral administrations of 100mg/kg body weight of AlCl3 and 1 mL/0.1 kg body weight of ACE for four weeks. When compared with vehicle-treated, AlCl3 administration caused a significant decrease in serum total protein (TP) and an increase in serum levels of alanine transaminase (ALT), aspartate transaminase (AST) and total bilirubin. On the other hand, ACE treatment significantly improved serum TP but depressed serum levels of ALT, AST and total bilirubin. There was no significant change in these biomarkers of liver function in ACE+AlCl3 group compared with the vehicle-treated group. Furthermore, while AlCl3 group was characterized by a significant rise in hepatic malondialdehyde (MDA) and a decrease in hepatic superoxide dismutase (SOD) and catalase activities, ACE group exhibited a significant low hepatic MDA and a high hepatic SOD and catalase activities. However, none of these antioxidant markers changed in ACE+AlCl3 group compared with vehicle-treated. Therefore, we conclude that ACE mitigates hepatotoxic effect of AlCl3 administration through regulation of hepatic oxidant/antioxidant system.