Five species of marine phytoplankton, Phaeodactylum tricornutum, Chaetoccros minutissimus, Platymunas suhcordiforinis, Nitzschia sp.and Dunaliella sp.were analyzed for the contents of total nitrogen, free amino acid and total amino acid.Their total nitrogen content was relatively high, ranging 3.37-7.6% and the total amino acid content 15.1-36.0%, Glu, Asp, Leu, Ala, Arg, and Gly being the main components.The free amino acid content in two species, Dunalietta sp.and Nitzschia sp.ranged 0.13-0.30%, in which Arg, Ala, Glu, and Asp were predominant.The crude protein in phytoplankton is high enough to be comparable with that of higher classes of seaweed such as Porphyra and Laminaria.