Melanin is a polymer of phenol which produces hyperpigmentation in the skin. Melanin synthesis is catalyzed by the enzyme tyrosinase. To investigate the whitening activity of the fractions from the ethanol extract of Enteromorpha linza, we studied the inhibitory effect on the tyrosinase activity and melanogenesis in the B16/F1 melanoma cells. The inhibition ratio of tyrosinase activity of ethylacetate fraction from E. linza was as strong as that of kojic acid, a positive control. Also, the melanin production was significantly inhibited by the ethylacetate fraction in a dose dependent manner. The ethylacetate fraction showed the highest activity in the fractions and as strong activity as that of arbutin, a positive control. From these results, we suggest that the E. linza extract might be able to apply to cosmetic and medical fields.