The biologically active component of licoris(Glycyrrhizae Radix L.) is considered to be glycyrrhetinic acid, an aglycone of glycyrrhizin, on the basis of chemical and pharmacological studies. The present study was undertaken to investigate the effect of glycyrrhetinic acid on the hepatic morphine-6-dehydrogenase activity, which catalize morphine to morphinone. Morphine-6-dehydrogenase was further purified by centrifugation, $(NH_4)_2SO_4$ fractionation, sephadex G-100, hydroxyapatite column. Hepatic morphine-6-dehydrogenase activity was significantly decreased by the treatment of glycyrrhetinic acid. When effect of glycyrrhetinic acid on the hepatic morphine-6-dehydrogenase was investigated in vitro, it was powerfully inhibited the enzyme activity with dose-dependent manner. From the above results, glycyrrhetinic acid inhibits hepatic morphine-6-dehydrogenase activity and decreases the morphine induced harmful side effects.