Human skin is constantly exposed to solar ultraviolet radiation (UVR). Skin has a unique ability to respond to UVR by increasing its pigmentation, a protective process driven by the melanogenesis of human epidermal melanocytes (HEMs). However, the molecular mechanisms used by HEMs to detect and respond to UVR remain unclear.We investigated the function and potential mechanism of opsin 5 (OPN5) in melanogenesis in HEMs.We used NaOH and L-DOPA methods to determine the melanin content and tyrosinase activity in HEMs, respectively. The expression of OPN5 in HEMs and explant tissues was detected by Western blotting (WB), reverse transcription PCR (RT-PCR) and immunofluorescence assays. RT-PCR and WB detected OPN5 expression levels in treated and untreated melanocytes. Subsequently, WB and RT-PCR were used to detect changes in the expression of tyrosinase (TYR) and tyrosine-related proteases (TRP1, TRP2) caused by changes in the OPN5 expression level. Moreover, changes in signalling pathway protein molecules were also tested.Here, we report that OPN5 is the key sensor in HEMs responsible for melanogenesis induced by UVR. OPN5-induced melanogenesis requires calcium-dependent G protein-coupled receptor and PKC signal transduction, thus contributing to the UVR-induced MITF response to mediate downstream cellular effects and providing evidence of OPN5 function in mammalian phototransduction. Remarkably, OPN5 activation is necessary for UVR-induced increase in cellular melanin and has an inherent function in melanocyte melanogenesis.Our results provide insight into the molecular mechanisms of UVR in melanocytes and may reveal molecular targets for preventing pigmentation or pigment diseases.