Abnormal pigmentation owing to excessive melanin synthesis can result in serious problems such as freckles, age-spots, and melanoma. Tyrosinase inhibitors have been an interesting target for the treatment of hyperpigmentation because tyrosinase is the rate-limiting enzyme in melanin synthesis. The screening for strong tyrosinase inhibitors led to the finding of the flavonoid galangin, which showed notable inhibitory effects on mushroom tyrosinase. The IC₅₀ value of galangin (3.55±0.39 µM) was lower than that of kojic acid (48.55±1.79 µM), which was used as a positive control. In silico docking simulation and mechanistic studies demonstrated that galangin interacted with the catalytic sites of tyrosinase and competed with tyrosine. In B16F10 melanoma cells stimulated with α-melanocyte stimulating hormone, galangin inhibited tyrosinase activity as well as melanin production. Although high doses of galangin were cytotoxic, no cytotoxic effects were observed at low doses. In addition, the in vivo efficacy of galangin was evaluated in HRM2 melanin-possessing hairless mice. As measured by the skin-whitening index and melanin staining, repeated UVB exposure increased skin melanin synthesis. Galangin application significantly reduced melanogenesis induced by UVB exposure. Collectively, our data indicates that galangin shows strong tyrosinase inhibition activity, which suggests that it may be an effective skin-whitening agent.