Fucoidan, a sulfated polysaccharide extracted from various brown seaweeds, possesses a wide range of pharmacological properties. In this study, we investigated the protective effect of fucoidan on acetaminophen-induced acute liver injury in rats. Liver injury was induced by administration of acetaminophen (800 mg/kg, i.p.) and fucoidan was administered (100 mg kg, p.o.) 2 h before and after acetaminophen administration. After 24 h, co-treatment of fucoidan ameliorated liver damage and cell death induced by acetaminophen. Acetaminophen induced the overexpression of CYP2E1, one of the metabolizing enzymes of acetaminophen, but cotreatment with fucoidan suppressed its increased expression of CYP2E1. Fucoidan also reduced the hepatic apoptosis induced by acetaminophen exposure as shown in the protein expression of Bax, Bcl-2, and cleaved caspase-3. The anti-oxidative effect of fucoidan was observed from the increase of the production and expression of glutathione, superoxide dismutase, and glutathione peroxidase, both of which were decreased by acetaminophen. Also, fucoidan decreased the expression of inflammatory mediators, including tumor necrosis factoralpha, interleukin 1 beta, and inducible nitric oxide synthase. Taken together, the data demonstrate the hepato-protective effects of fucoidan against acetaminophen-induced liver injury via anti-oxidant, anti-inflammatory, and anti-apoptotic mechanisms.