Gas chromatography method was used to determine the content of fatty acids in eight Sargassum species from Guangxi Beibu Bay for comparison with that of Laminaria japonica, Porphyra yezoensis Veda and Ulva pertusa Kjellm. The results were as follows: 1. The predominant saturated fatty acid in all Sargassum were palmitic acid (16: 0)whose content was about 33-50% of total fatty acids. 2. The composition of C18 polyunsaturated fatty acids (PUFA) in the Sargassum were more than that of Porphyra vezoensis. Main PUFA were Linoleic acid (18: 2ω6, LA) and Alpha-Linolenic acid (18: 3ω3, ALA) whose average content comprised 21-26% of total fatty acids. Eicosatetraenoic acid (Arachidonic acid, 20: 4ω6, AA) and Eicosapentaenoic acid (20: 5ω3, EPA) are useful for the human body and comprise 10% (average content)in Sargassum, 5.3-14.7% of them is AA, 1.14-3.78% is EPA.3. The content of PUFA in Sargassum was higher than that in Laminaria japonica and the some as that in Ulva pertusa Kjellm. In these seaweeds studied Porphyra vezoenosis has the highest PUFA content.