Tyrosinase catalyzes the rate-limiting steps in melanin biosynthesis which is involved in skin-coloring and local hyperpigmentation of human beings, and unfavorable darkening of food products, Inhibitory effects on 3,4-dihydroxy-phenylalanine (dopa) oxidase activity of tyrosinase by 594 kinds of herbal extracts prepared from herbal medicines and wild plants in Korea were estimated. Two herbal extracts prepared from radicis cortex of Morus alba and rhizoma of Curcuma longa were selected as those exhibiting potent inhibitory effects on the enzyme activity. These herbal extracts were subjected to sequential fractionations with methylene chloride, ethyl acetate, n-butanol, and polar residue. The inhibitory effects on dopa oxidase activity of tyrosinase were shown in ethyl acetate fraction of Morus alba, and in methylene chloride fraction of Curcuma langa. The ethyl acetate fraction of Marus alba exhibited 50% of inhibition on dopa oxidase activity of tyrosinase at the concentration of 12 ${mu}g/ml$, and methylene chloride fraction of Curcuma langa at 51 ${mu}g/ml$.