For the biological survey, effects of Ailanthi Cortex Radicis, the root bark of Ailanthus altissima(Simaroubaceae) on epoxide hydrolyzing enzymes were checked. The methanolic extract and its chloroform fraction were shown to activate the liver metabolizing enzyme system including epoxide hydrolase system which was monitored by activities of transaminase, lactate dehydrogenase, alkaline phosphatase and epoxide hydrolase system in bromobenzene treated rats. But they showed no effect on glutathione S-transferase activity.