The results of screening of biologically active principles in Chinese medicinal prescriptions used for the treatment of hepatic jaundice suggested the presence of strong inhibitors of β-glucuronidase in "Inchinko-to"extracts. Non-dialyzable portion (A-6) of water-soluble fraction of"Inchinko-to"extracts was found to be potently inhibitory against β-glucuronidase from bovine liver. The inhibitor of β-glucuronidase was partially purified by gel-filtration on Toyopearl HW-60S and column chromatography on DEAE-cellulose. The partially purified β-glucuronidase inhibitor (A-8) was supposed to be a glycoprotein or a glycopeptide. Its activity was not affected by acid, pepsin and trypsin. It also inhibited β-glucuronidase obtained from human intestinal bacteria.