In this study, we examined the effect of a hot-water extract of coccolithophore Pleurochrysis carterae on melanogenesis in B16F1 and B16F10 melanoma cells. P. carterae extract inhibited the α-melanocyte stimulating hormone (α-MSH)-enhanced melanin synthesis in B16F1 melanoma cells. P. carterae also inhibited unstimulated melanin synthesis in B16F10 melanoma cells. Western blotting showed that the P. carterae extract inhibited tyrosinase and microphthalmia-associated transcription factor (MITF) in a dose-dependent manner. The reporter assay also revealed a decline in the tyrosinase promoter activity in the presence of P. carterae extract. Furthermore, quantitative real-time RT-PCR analysis showed that P. carterae extract down-regulated the mRNA levels of tyrosinase and MITF. Finally, our study demonstrated that the hot water extract of P. carterae inhibits melanin synthesis via the down-regulation of MITF mRNA level. Our findings indicate that P. carterae extract could be a possible cosmetic ingredient.