Sulfated polysaccharides (SPs) were identified in different portions of the thallus of Sargassum plagiophyllum C. Agardh, with TBO staining. SPs were extracted using a blade and purified by Q sepharose fast flow anion-exchange chromatography, resulting in SP fractions F1, F2 and F3, with molecular weights of 30,35 and 20 kDa, respectively. An SP yield of 43.1% was obtained in F3, while F2 yielded a sulfate content of 21.9%. Furthermore, the in vitro anticancer and antioxidant activities of the polysaccharide fractions were evaluated. The F2 fraction showed higher anticancer activity against HepG2 and A549 cells than the other two fractions, with IC50 values of 600 mu g/mL and 700 mu g/mL, respectively. The normal breast epithelial cell line (HBL-100) exhibited IC50 concentrations of 1200 and 1400 mu g/mL for crude sulfated polysaccharides (CSPs) and all SP fractions (F1-F3). These results indicated that the anticancer activity of F2 could be related to its sulfate content. However, the antioxidant activities of F1-F3 were low at their tested concentrations. (C) 2012 Elsevier Ltd. All rights reserved.