This study was carried out to investigate the inhibiton effects of Coprinus comatus ethanol extract of edible mushroom on liver damage in benzo(a)pyrene (B(a)P) treated mice. The activities of serum aminotransferase, cytochrome P 450 and hepatic content of lipid peroxide after B(a)P treatment were increased than those of control, but those levels were significantly decreased by the treatment of Coprinus comatus ethanol extract. Whereas, the hepatic glutathione content and glutathione S transferase activity were decreased by B(a)P treatment than those of control, but those were increased by the treatment of Coprinus comatus ethanol extract. Also the activities of superoxide dismutase, catalase and glutathione peroxidase after B(a)P treatment were markedly increased than those of control, but those levels were decreased by the treatment of Coprinus comatus ethanol extract. These results suggest that Coprinus comatus ethanol extract have a protective effect on liver damage by benzo(a)pyrene through the mechanisms of decreasing lipid peroxide and activities of free radical generating enzymes.