The ethylacetate fraction of the overground portion of Polygonum aviculare L. exhibited the anti-lipid peroxidation and the liver protective effect in intoxicated rats. Through silica gel chromatography of the ethylacetate fraction monitered by bioassay, two flavonoids, avicularin and juglanin were isolated as active components. Avicularin and juglanin remarkablely inhibited the lipid peroxidation of rat liver induced by 50% ethanol. Especially avicularin exhibited the stronger anti-lipid peroxidation effect than juglanin. Avicularin as a main principle of Polygonum aviculare L. significantly exhibited liver protective activities by decreasing s-GOT and s-LDH levels which represent for the hepatotoxicity induced by $CCl_4$ in rats. In addition, avicularin significantly decreased not only s-LDH but also s-bilirubin levels in intoxicated rat induced by ${alpha}-naphthylisothiocyanate;(ANIT)$. These results suggest that avicularin has the protective effects against the hepatoxicity induced by $CCl_4$ and ANIT in rats.