Albinism is a phenomenon that color of the body surface is changed to white orfaint brown from the specific color to the species by difficiency of pigments due to mutation or disease. This study was undertaken to investigate the experimental basis on the appearance of albinism in cultured flounder Paralichthys olivaceus. The skin and muscle from the normal and albinic flounder were used by measuring contents of amino acid free amino acid. The results were summarized as follows: Contents of amino acid in theskin and muscle are different from normal and albinic flounder. Phenolic and sulfuric amino acids in the skin of normal flounder were 2 times those of albinic ones. Especially tyrosine contents of the skin in normal flounder were 24 times higher than those. Methionine was 26 times higher than those Phenylalanine was 1.6 times higher. In free amino aicd phosphoserine and phosphoethanolamine were a little higher than that ones. The melanin formation of the skin in flounder was affected by substrates such as phenolic amino acid and cofactor such as sulfuric amino acid.