The methanol extracts of some marine algae were tested for investigating the effects on the formation of lipid peroxide and the activities of free radical generating enzyme in vitro in bromobenzene-treated rat. The extracts of Enteromorpha compressa, Capsosiphon fulvescens, Gelidium amansii, Hizikia fusiformis, Sargassum siliquastrum and Sargassum thunbergii which decreased the formation of lipid peroxide, inhibited the activity of xanthine and aldehyde oxidases by adding of each extracts. Phloroglucinol isolated from Ecklonia stolonifera reduced bromobenzene-induced hepatic lipid peroxidation. This compound administered daily over one week before intoxication with bromobenzene did not affect the activities of aminopyrine N-demethylase, aniline hydroxylase and glu tathione S-transferase. Epoxide hydrolase activity was decreased by bromobenzene, which was restored by pretreatment of phloroglucinol, The results suggest that the bromobenzene-induced hepatic lipid peroxidation by phloroglucinol is reduced by enhancing the activity of epoxide hydrolase.