Phloroglucinol isolated from Ecklonia stolonifera prevented the acetaminophen (800 mg/kg, i.p.)-induced rats as evidenced by the decreased formation of lipid peroxide. The activities of cytochrome P-450, animopyrine N-demethylase and aniline hydroxylase were not changed by the treatment with phenolic compound as compared with acetaminophen-treated rats. The glutathione S-transferase activity was decreased by the treatment of acetaminophen. This enzyme activity was restored in liver of pretreated-rats given by phloroglucinol. Pretreatment of this compound marked the liver protective activities as recovering the decreased glutathione level and glutathione reductase activity in rats treated with acetaminophen. But gamma-glutamylcystein synthetase activity was not changed. The results suggest that the acetaminophen-induced hepatic lipid peroxidation may be reduced by enhancing the activity of glutathione S-transferase.