The fatty acid composition of the lipoid extracts of four marine alga species, Halopteris scoparia (L.) Sauvagau, Scinaia furcellata L., Sargassum natans (L.) J. Meyer, Padina vickersiae Hoyt, and the sea grass Posidonia oceanica L. as well as six freshwater alga species, namely Cladophora fracta (Dilw.) Kutz, C. glomerata (Dilw.) Kutz, Zygnema pectinatum (Vauch.) C. A. Agardh, Maugeotia sp. (C. A. Agardh), Vaucheria sessilis (Vauch.) De Candolle, and Spyrogyra gratiana Link. together with the aquatic plant Potomogeton perfoliatus L., collected from Turkish waters, was characterized by capillary GC-MS. Only the saturated fatty acids were found in the species investigated.