Inhibitors of melanin biosynthesis were screened by using three different methods. The extract of Veratrum patulum contains hydroxystilbene compounds that are potent tyrosinase inhibitors. We evaluated the enzyme inhibitory property on the mushroom tyrosinase of hydroxystilbene compounds including resveratrol, oxyresveratrol, and their analogs. Biotransformation using cellulase of the whole extract brought about an increase in the inhibitory activity of the products on mushroom tyrosinase. The enhancement of tyrosinase inhibition is supposed to increase the concentration of aglycon, which has superior inhibitory activity to its glycoside. Eventually, melanin biosynthesis was inhibited by the enhanced tyrosinase inhibitory activity of the extract. This result indicated that deglycosylation of stilbene compounds has exerted more effective inhibition on the enzyme than that of the unprocessed plant extract. © 2004 Wiley Periodicals, Inc.