Petasites japonicus (Compositae) is a perennial herb which has been used as treatment of antitussive, expectorant, sedatives, paralysis, diurectics in folk remedies. The pharmacological studies of this natural drug have not yet estabilished. So, we examined anti-lipid peroxidative effects and liver protective effect on CCl4 induced lipid peroxidation and hepatotoxicity in rats. In vivo liver lipid, MeOH Ex. revealed significant increase of anti-lipid peroxidative effects according to concentration dependently. In chemical parameters obtained from serum analysis, MeOH Ex. as a increase of medicine concentration (0.25 g/kg, 0.5 g/kg, 1.0 g/kg), GOT, GPT, AlP decreased. In 0.5 g/kg GPT administered group, there was relative in GOT, AlP. Cholesterol decreased in 1.0 g/kg and 1.0 g/kg administered group, BUN decreased relatively in 1.0 g/kg administered group.