Several compounds and extracts isolated from a brown alga, Ishige (I.) okamurae, exhibit anti-oxidant and anti-inflammatory effects. The present study investigated whether the ethyl acetate (EtOAc) fraction of I. okamurae (EFIO) could ameliorate carbon tetrachloride (CCl₄)-induced hepatotoxicity in rats. Sprague-Dawley rats were intraperitoneally (i.p.) administered with EFIO at 10 or 50 mg/kg per day for 2 consecutive days before CCl₄ injection (3.3 mL/kg, i.p.). Twenty four hours later, the rats were anesthesized with diethyl ether and dissected. Pretreatment with EFIO significantly reduced the increased serum levels of alanine aminotransferase and aspartate aminotransferase in CCl₄-treated rats. Pretreatment with EFIO also significantly inhibited the reduced activities of superoxide dismutase and catalase in the CCl₄-injured liver. Histopathological evaluations showed that hemorrhage, hepatocyte necrosis, inflammatory cell infiltration, and fatty degeneration induced by CCl₄ treatment were ameliorated by the administration of EFIO. Additionally, liver immunohistochemical analyses revealed the marked reduction in ED1-positive monocyte-like macrophages in EFIO-pretreated rats given CCl₄. These results suggest that EFIO ameliorates CCl₄-induced liver injury, possibly through the inhibition of oxidative stress.