As a part of pharmacological studies of saikosaponins, which were reported to exhibit diverse biological activities especially concerning with liver function, effects of saikosaponin on metabolizing enzymes and lipid peroxide contents in liver were examined. As the result, UDP-glucose dehydrogenase activity and lipid peroxidation which were due to acetaminophen were inhibited by saikosaponin treatment. But other metabolizing enzyme activities were not modified.