Albinos in Japanese flounder Paralichthys olivaceus are yellowish mutants which lack melanophores. To reveal the function of melanophores, U V-B tolerance was compared between wild-Type (1 00±8 mm) and albino (98 ± 6 mm) flounder juveniles. After 6 hours of U V-B exposure (1.1 W/m2), survival was examined every 1 hour for 24 hours. Control treatment without UV exposure was also conducted. Albino fish in the UV treatment showed significantly lower survival than that of wild-Type fish. There was no significant difference in survival between strains in the control. Present research suggests that melanophores have a UV photoprotective function in flounder juveniles.