Melanogenesis inhibitory and free radical scavenging activities of nine cyclic (1—9) and one acyclic diarylheptanoids (10), and two phenolic compounds, (+)-rhododendrol (11) and (+)-catechin (12), isolated from the ethyl acetate-soluble fraction of the MeOH extract of the bark of Acer nikoense MAXIM. (Aceraceae) were examined. Upon evaluation of compounds 1—12 on the melanogenesis in the B16 melanoma cells, two compounds, 2 and 8, exhibited marked inhibitory activity with 55.6% and 46.8% reduction, respectively, of melanin content at 25 μg/ml without inhibition of cell proliferation. In addition, upon an evaluation of eleven compounds, 1—7 and 9—12 against the scavenging activities of free radicals (against the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical), compound 12 (IC₅₀ 9.0 μM) followed by compounds 1, 3, 4, and 6 (IC₅₀ 40.2—44.0 μM) showed potent scavenging activities.