The bioassay-guided fractionation of the methylene chloride soluble portion of a methanol extract of Machilus thunbergii bark led to the isolation of four known lignans, machilin A (1), meso-monomethyl dihydroguaiaretic acid (2), nectandrin A (3) and nectandrin B (4), which exhibited potent inhibitory activity on melanin biosynthesis in cultured B-16 mouse melanoma cells (IC(50): 39.9, 15.1, 19.4 and 37.8 microM, respectively).