The in vitro antioxidant and in vivo hepatoprotective effects of aqueous extract of Allium cepa (A. cepa) bulb were evaluated in male rats against ethanol induced liver damage in preventive and curative models. The antioxidant activity of A. cepa was assayed and activities were compared to standard antioxidant, ascorbic acid. The results revealed that the IC₅₀ values of A. cepa bulb extract for DPPH, hydroxyl, superoxide radical scavenging activities were 195.2 ± 0.2, 374.7 ± 0.4 and 182.5 ± 1.7 μg/mL, respectively. Liver injury was induced by 40% ethanol administration (3.76 g/kgbw, orally) for 25 days. In two different sets of experiments, the A. cepa extracts (100, 300 and 600 mg/kg bw) and silymarin (100 mg/kg bw) were administered orally in preventive and curative models. Ethanol administration caused severe hepatic damage in rats as evidenced by elevated serum aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP) and total bilirubin levels. The A. cepa and silymarin administration prevented the toxic effect of ethanol on the above serum parameters in both preventive and curative models. The present study concludes that aqueous extract of A. cepa bulb has significant antioxidant and hepatoprotective activity against ethanol induced hepatotoxicity.