Royal jelly composes of many components, especially protein. Protein is a major factor which cause allergy. We focused on water soluble royal jelly (WSRJ) that was removed allergy - inducing protein. 10-hyroxy-2-decenoic acid content of WSRJ is 2.42 g/100 g, which is double compared to that of lypophilized RJ. To further access WSRJ as a cosmetic ingredient and potential external treatment for topical use, we investigated its ability to inhibit tyrosinase activity and melanin biosynthesis on melanogenesis in B16F1 melanoma cells. We found that WSRJ increased the cell viability in B16F1 melanoma cell and WSRJ (1~10 mg/ml) inhibited melanin synthesis in with 10 nM ${alpha}$-melanocyte-stimulating hormone (${alpha}$-MSH) for 48 h. WSRJ inhibited direct tyrosinase activity, which decreased melanin synthesis in ${alpha}$-MSH stimulated B16F1 melanoma cells. Thease findings suggest that WSRJ induces the down regulation of melanogenesis by inhibiting tyrosinase activation.