From an industrial viewpoint, the pure culture of the protist Thraustochytrium sp.CHN-1 (labyrinthulids) isolated from the Seto Inland Sea was cultivated and chemical analysis was performed to clarify itscomposition of useful substances (pigments, fatty acids, amino acids, monosaccharides and sterols).These results showed that Thraustochytrium sp. CHN-1 has a higher C/N value than other marine organisms, that it is carbon-rich and is composed of half lipids.Fatty acids that constitute the lipids were mostly C18: 1, C22: 6 and C22: 5. The lipid fraction contained free astaxanthin and cholesterol.Carbohydrates were characterized by the abundance of galactose. Regarding vitamin content, it was rich in biotin, nicotinamide, and vitamin C. In the future, the characteristic composition of useful substances can be used in determining feed for animals, aquaculture, and so on.