AIMS: Sulfated polysaccharide extracted from the brown algae Sargassum swartzii was studied for antioxidant potential. METHODS: The extracted sulfated polysaccharide was analyzed for physico-chemical characteristics, TAC, reducing power, free radical scavenging potentials (DPPH, ABTS, H2O2 radical) and antibacterial properties. RESULTS: The extract showed a high percentage of carbohydrate (7.40 ± 0.63) %, followed by sulfate (5.3 ± 1.54) %. The highest antioxidant activity was observed in ABTS (55 ± 3.61) %, followed by H2O2 (47.23 ± 2.81) % and DPPH (25.33 ± 2.52) %; significant differences were observed at (P ≥ 0.05). Among the ten human pathogenic strains tested, E. coli was the more sensitive. The characterization and mobility of the sulfated polysaccharide was examined by the FT-IR spectrum and assayed by agarose gel electrophoresis which showed highest mobility at higher pH buffer in carbonate-bicarbonate (pH 10) buffer. The molecular weight of the sulfated polysaccharide was determined by gradient PAGE and was found to be 50 KDa. Finally, GC-MS analysis revealed the presence of peaks corresponding to dimethyl-4-nitroaniline (26.34%). CONCLUSIONS: It is suggested that the sulfated polysaccharide from Sargassum swartzii could be a better source of natural antioxidant, as well as an antibacterial agent. METHODS: The extracted sulfated polysaccharide was analyzed for physico-chemical characteristics, TAC, reducing power, free radical scavenging potentials (DPPH, ABTS, H2O2 radical) and antibacterial RESULTS: The extract showed a high percentage of carbohydrate (7.40 ± 0.63)%, followed by sulfate (5.3 ± 1.54)%. The highest antioxidant activity was observed in ABTS (55 ± 3.61)%, followed by H2O2 2.81)% and DPPH (25.33 ± 2.52)%; significant differences were observed at (P ≥ 0.05). Among the ten human pathogenic strains tested, E. coli was the more sensitive. The characterization and mobility of the sulfated polysaccharide was examined by the FT-IR spectrum and assayed by agarose gel electrophoresis which showed highest mobility at higher pH buffer in carbonate-bicarbonate (pH 10) buffer. The molecular weight of the sulfated polysaccharide was determined by gradient PAGE and was found to be 50 KDa. Finally, GC-MS analysis revealed the presence of peaks corresponding to dimethyl-4-nitroaniline (26.34%). CONCLUSIONS: It is suggested that the sulfated polysaccharide from Sargassum swartzii could be a better source of natural antioxidant, as well as an antibacterial agent.