| Summary: | <i>Nostoc verrucosum</i>, an edible microalgal species, forms colonies in streams. Here, we investigated the antimelanogenic and anti-oxidative effects of <i>N. verrucosum</i> extracts. We collected <i>N. verrucosum</i> from Toyama Prefecture, Japan, and successfully cultured it in indoor cultivation systems. Aqueous, methanol, and hexane extracts of <i>N. verrucosum</i> were prepared for various experiments. To elucidate the antimelanogenic effects of <i>N. verrucosum</i>, we performed tyrosinase assay, melanin content assay, western blotting, and real-time quantitative reverse-transcription polymerase chain reaction (qRT-PCR). Anti-oxidative effects were evaluated using the 2,2’-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid (ABTS) assay. The methanol and hexane extracts significantly inhibited melanin synthesis in B16F1 melanoma cells. Western blotting showed that 12.5 and 25.0 µg/mL <i>N. verrucosum</i> hexane extract suppressed tyrosinase activity. The qRT-PCR analysis revealed that <i>N. verrucosum</i> hexane extract inhibited α-melanocyte stimulating hormone-enhanced <i>tyrosinase</i>, tyrosinase-related protein (<i>TRP</i>)-1, <i>TRP-2</i>, and melanocortin 1 receptor (<i>MC1R</i>) mRNA expression. On the contrary, <i>N. verrucosum</i> hexane extract did not alter microphthalmia-associated transcription factor (<i>Mitf</i>) transcription. The ABTS assay showed that all extracts had radical scavenging activities, and the IC<sub>50</sub> values of the aqueous and methanol extracts were 294.6 and 172.8 µg/mL, respectively. Our findings demonstrate that <i>N. verrucosum</i> is a suitable candidate for the development of antimelanogenic agents, cosmetics, or functional food ingredients.
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