BACKGROUND Melanoma is one of the most aggressive types of cancer and it has shown a remarkable surge in incidence during the last 50 years. Melanoma has been projected to be continuously rising in the future. Therapy for advanced-type melanoma is still a challenge due to the low response rate and poor 10-year survival. Interestingly, several epidemiological and preclinical studies had reported that vitamin D deficiency was associated with disease progression in several cancer types. In vivo and in vitro studies revealed anti-proliferative, anti-angiogenic, apoptosis, and differentiation induction effects of calcitriol in various cancers. However, information on the effects of calcitriol (1,25(OH)₂D₃) on melanoma is still limited, and its mechanism remains unclear. MATERIAL AND METHODS In the present study, by utilizing B16-F10 cells, which is a melanoma cell line, we explored the anti-proliferative effect of calcitriol using cell viability assay, near-infrared imaging, expression of apoptosis-related genes using real-time polymerase chain reactions (PCR), and the expression of apoptosis proteins levels using western blot. In addition, we also assessed calcitriol uptake by B16-F10 cells using high-performance liquid chromatography (HPLC). RESULTS We found that calcitriol inhibits melanoma cell proliferation with an IC₅₀ of 93.88 ppm (0.24 μM), as shown by cell viability assay. Additionally, we showed that B16-F10 cells are capable of calcitriol uptake, with a peak uptake time at 60 min after administration. Calcitriol was also able to induce apoptosis-related proteins such as caspase-3, caspase 8, and caspase-9. These effects of calcitriol reflect its potential utility as a potent adjuvant therapy for melanoma. CONCLUSIONS Calcitriol inhibits cell proliferation and induces apoptosis in B16-F10 cells.