Down-regulation of melanin synthesis is required for recovery of pigmentary disorders and it is known that direct inhibitors of tyrosinase suppress melanin synthesis. We screened several oriental medicinal plants using B16/Fl0 cells and found that the methanolic extract of Cnidii Rhizoma down-regulated melanin synthesis effectively. Although the proliferation of Bl6/Fl0 cells was decresed by the methanolic extract of Cnidii Rhizoma, it did not appear necrosis. Bl6/F10 cells incubated with the methanolic extract of Cnidii Rhizoma showed reduced pigmentation and tyrosinase activity. Western blotting revealed that the amount of tyrosinase was decreased by the methanolic extract of Cnidii Rhizoma. These results suggest that the inhibitary effect of the methanolic extract of Cnidii Rhizoma on melanogenesis is due to the suppression of tyrosinase in Bl6/F10 cells and Cnidii Rhizoma is a candidate for an efficient whitening agent.