The protective effect of Hericium erinaceus methanol extract was investigated on benzo($alpha$)pyrene(B($alpha$)P) induced hepatotoxicity in mice, Hericium erinaceus extract was intraperitioneally injected once a hay for successive 5 days. followed by treatment with B($alpha$)P on the fifth day. The elevated activities of serum aminotransferase and hepatic cytochrome P-450 by B($alpha$)P was decreased by pretretament with Hericium erinaceus extract. Moreover, hepatic lipid peroxide content and glutathions S-transferase activity increased by B($alpha$)P were significantly decrease, but depletion of glutathione content induced by B($alpha$)P was prevented by Hericium erinaceus extract. In addition, the increased activities of superoxide diamutase, catalase and glutathions peroxidase after B($alpha$)P-treatment were decreasd. Immunoblott analysis of hepatic microsomes showed that methanol extract of Hericium erinaceus suppressed protein level of the cytochrome P-450 1AI increaed by B($alpha$)P. These results suggest that Hericium erinaceus extract may protect liver from damage induced by B($alpha$)P.