en Biotechnology Biotechnology پژوهشي Orginal research papers The chemical compositions, antioxidant and antimicrobial properties of fucoidan extracted from <em>Sargassum ilicifolium</em> and <em>Sargassum angustifolium </em>were investigated. The results showed that these seaweeds were characterized by an acceptable level of minerals and proteins. The fatty acid profile was dominated by the palmitic acid, which represents about 37.44&plusmn;0.01% and 23.05&plusmn;0.01% of the total fatty acids, followed by oleic acid (13.83&plusmn;0.01% and 45.30&plusmn;0.01%) for <em>S. ilicifolium</em>and <em>S. angustifolium</em>, respectively. Swelling capacity, water holding capacity and oil holding capacity were varied in two different temperatures (25^◦C and 37^◦C).The antioxidant activities of fucoidan including DPPH, superoxide-hydroxyl radical scavenging, chelating ability and reducing power were considerable. The correlation of sulfate and phenol contents with scavenging superoxide radical ability, chelating ability and reducing power was positive. The antibacterial activity was evaluated by disc diffusion method against <em>Bacillus subtilis</em> and <em>Staphylococcus </em><em>aureus </em>(gram positive bacteria) and <em>Escherichia coli</em> and <em>Salmonella enteritidis </em>(gram negative bacteria). There were no positive results against gram negative bacteria. In the concentration of 5 mg ml^-1small clear inhibition zones was observed against B. <em>subtilis</em> and <em>S.aureus</em><em>. </em>On the basis of obtaining results from antioxidant activities, fucoidanis suggested as potential natural and safe antioxidant agents in the nutraceutical industry. Fucoidan, Antioxidant, Antimicrobial, Brown seaweed, Sargassum. 457 475 http://jifro.ir/browse.php?a_code=A-10-1192-7&slc_lang=en&sid=1 M. Kordjazi moazamehkordjazi@gmail.com 100319475328460031194 100319475328460031194 Yes Faculty of Fisheries Science, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran. Y. Etemadian y.etemadian@gmail.com 100319475328460031195 100319475328460031195 No Faculty of Fisheries Science, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran. B. Shabanpour shabanpourbahareh@gmail.com 100319475328460031196 100319475328460031196 No Faculty of Fisheries Science, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran. P. Pourashouri ppourashour@gmail.com 100319475328460031197 100319475328460031197 No Faculty of Fisheries Science, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran.