In order to screen microalgal species for higher contents of poly-unsaturated fatty acids, two marine microalgae, Phaeodactylum tricomutumand Isochrysis galbana, were cultured in indoor and their fatty acids composi-tion was examined. The results showed that C16:0, C16:1 and C20:5(EPA)were rich, and little C20:4 and no C22:6(DHA) were detected in Phaeodac-tylum tricornutum. PUFAs accounted for 23 .8% of the total fatty acids in thisspecies. However, the major fatty acids of Isochrysis galbana were C14: 0,C16:0, C16:2, C18:3 and C22:6(DHA). EPA was little and C20:4 wasnot detected, and PUFAs were up to 49.8% of the total fatty acids in this al-ga. The two species of marine microalgae showed significant differences in fat-ty acids composition.