Melanocytes are pigment-producing cells responsible for coloration of skin and hair. Although the importance of Wnt3a in melanocyte development has been well recognized, the role of Wnt3a in mature melanocytes has not been elucidated. This study was conducted to further explore the effects of Wnt3a on melanocyte proliferation and melanogenesis, and to elucidate the possible mechanisms involved. We infected melan-a cells with AdWnt3a to serve as the production source of the Wnt3a protein. MTT assay, 5-bromodeoxyuridine incorporation assay and flow cytometric analysis showed that Wnt3a inhibited the proliferation of melan-a cells and this was associated with decrease of cells in the S phase and increase of cells in the G(1) phase. Melanin content and tyrosinase activity assay revealed that Wnt3a significantly promoted melanogenesis of melan-a cells. Furthermore, western blot analysis showed that Wnt3a upregulated the expression of microphthalmia-associated transcription factor and its downstream target genes, tyrosinase and tyrosinase-related protein 1 in melan-a cells. Collectively, our results suggest that Wnt3a plays an important role in melanocyte homeostasis.