This study was conducted to evaluate the effects of Glycyrrhizae Radix water extract, known as depigmenting agent, on melanin biosynthesis in cellular level. The inhibitory effect of Glycyrrhizae Radix water extract on melanogenesis was identified by mushroom tyrosinase assay, To determine whether Glycyrrhizae Radix water extract suppress melanin synthesis in cellular level, B16 mouse melanoma cells were cultured in the presence of different concentrations of Glycyrrhizae Radix water extract. The maximum concentration of Glycyrrhizae Radix water extract that was not inhibitory to growth of the cells was 2 mg/ml. At that concentration, melanin synthesis was significantly inhibited without cytotoxicity after 5 days, compared with untreated cells. The treatment with Glycyrrhizae Radix water extract reduced tyrosinase and DOPAchrome tautomerase activity in a dose-dependent manner. These results suggest that the inhibitory effect of Glycyrrhizae Radix water extract on melanogenesis is due to the suppression of tyrosinase and DOPAchrome tautomerase activity.