Objective: To find anti-melanogenesis materials used in whitening cosmetics.Methods: The ethanolic leaf extract of Mallotus japonicus(M. japonicus) having an anti-melanogenesis activity was separated by a sephadex LH-20 chromatography. Each fraction was measured for its tyrosinase inhibitory activity together with its polyphenol content using the Folin–Ciocalteu method. The anti-melanogenesis activity of the active fractions was determined by the melanin content in the murine B16F1 melanoma. The active fractions were put together due to similar constituents, and then separated by high performance liquid chromatography using a C-18 ODS column. The major antimelanogenesis compound was identified using1 H and13C-NMR and liquid chromatography-mass spectrometry.Results: The ethanolic leaf extract of M. japonicus showed an anti-tyrosinase activity with a high polyphenol content, resulting in suppression of melanin production in the B16F1 melanoma. The extract was separated and the active compound was identical as rutin based on the1 H,13C-NMR and liquid chromatography-mass spectrometry analysis data. In addition, the rutin treatment with cells reduced the melanin content in a concentration dependent manner without any cell toxicity. The leaf extract of M. japonicus containing rutin would be useful in whitening cosmetics for protection from UV-light exposure to be limiting the accumulation of melanin in skin.Conclusions: The leaf extract of M. japonicus and/or rutin isolated from the extract as a key whitening agent would be useful as a whitening cosmetic material for protecting against disorder skin due to melanin accumulation. Objective: To find anti-melanogenesis materials used in whitening cosmetics. Methods: The ethanolic leaf extract of Mallotus japonicus (M. japonicus) having an anti-melanogenesis activity was separated by a sephadex LH-20 chromatography. Each fraction was measured for its tyrosinase inhibitory activity together with its polyphenol content using the Folin-Ciocalteu method. The anti-melanogenesis activity of the active fractions was determined by the melanin content in the murine B16F1 melanoma. The active fractions were put together due due to similar constituents, and then separated by high performance liquid chromatography using a C-18 ODS column. The major antimelanogenesis compound was identified using1H and13C-NMR and liquid chromatography-mass spectrometry. Results: The ethanolic leaf extract of M. japonicus showed an anti-tyrosinase activity with a high polyphenol content, resulting in suppression of melanin production in the B16F1 melanoma. The extract was separated and the active c ompound was identical as rutin based on the1 H, 13C-NMR and liquid chromatography-mass spectrometry analysis data. In addition, the rutin treatment with cells reduced the melanin content in a concentration dependent manner without any cell toxicity. japonicus containing rutin would be useful in whitening cosmetics for protection from UV-light exposure to be limiting the accumulation of melanin in skin. Conclusions: The leaf extract of M. japonicus and / or rutin isolated from the extract as a key whitening agent would be useful as a whitening cosmetic material for protecting against disorder skin due to melanin accumulation.