To discover an active skin depigmentation agent, we isolated a melanin biosynthesis inhibitor from the methanol extract of astragalus (Astragalus membranaceus) using a bioactivity-guided fractionation and identified it as calycosin-7-O-${eta}$-D-glucoside via spectroscopic analysis. The active compound exhibited tyrosinase inhibitory activity with an $IC_{50}$ value of 68 ${mu}M$. In addition, calycosin-7-O-${eta}$-D-glucoside showed a melanin biosynthesis inhibition zone in a culture plate of Streptomyces bikiniensis. Furthermore, 75.78 ${mu}M$ of calycosin-7-O-${eta}$-D-glucoside dramatically decreased 50% of the melanin content on Melan-a cells without any apparent cytotoxicity. Theses results indicate that the calycosin-7-O-${eta}$-D-glucoside isolated from astragalus may be a good candidate for skin-whitening agent.