OBJECTIVES: Arsenic (As) is ubiquitously distributed in the environment and is known as a human carcinogen. In this study, acute As toxicity at lethal dosage in rats and mice was evaluated, and As-induced hepatotoxicity was characterized. METHODS: Male Sprague-Dawley rats, male ICR mice and trivalent inorganic As, sodium arsenite, were used in this experiment. LD50 and LD100 were calculated from 24-hour lethality after the single subcutaneous administration of As into rats and mice. Serum and liver were collected from the surviving animals. The activities of ALT, AST and gamma-GT in serum were determined, and the concentrations of MDA, GSH and CYP450 in liver were analyzed. RESULTS: The LD50 and LD100 of sodium arsenite were calculated as 12 mg/kg and 13 mg/kg for rats, and 16.5 mg/kg and 19 mg/kg for mice, respectively. Thus, the rat was more susceptible than the mouse to the acute lethal toxicity of As. The histopathological changes induced by As were similar between rats and mice. AST was increased in high-dose As-treated rats and mice, whereas ALT was increased in high-dose As-treated mice but not in rats. gamma-GT was not significantly changed between the two animal groups. As increased lipid peroxidation, but decreased GSH and CYP450 in the liver of both rats and mice, in dose-dependent patterns. These results indicate that oxidative stress might be one of the mechanisms in As-induced hepatotoxicity. CONCLUSION: Rats were more susceptive than mice to acute As toxicity, and oxidative stress might play a part in liver injury induced by As.