The effects of methanol extract of the leaves of Brassica juncea and its major component, isorhamnetin 3-O-${eta}$-D-glucopyranoside on hepatic alcohol metabolizing enzymes were investigated. The methanol extract and isorhamnetin 3-O-${eta}$-D-glucopyranoside supplementations increased the activities of microsomal ethanol oxidizing system and aldehyde dehydrogenase in a dose-dependent manner, and had mild effects on the activities of alcohol dehydrogenase and catalase. Isorhamnetin 3-O-${eta}$-D-glucopyranoside alleviated the adverse effect of ethanol ingestion by enhancing the activities of alcohol oxidizing emzymes, microsomal ethanol oxidizing system and aldehyde dehydrogenase.