Most species of brown seaweed (Phaeophyta) get high economic value and a great number of uses, in which products extracted from Sargassum genus have been widely used in different fields such as food, medicine and industry all over the world during years ago. Brown seaweed Sargassum are now being considered to be a rich source of antioxidants and nutrients from the ocean. It has been reported that polysaccharide extracted from Sargassum to be the potential source of andioxidants that used as immunostimulants for aquatic animals health enhancement. Among brown seaweed species, Sargassum microcystum is a common plant which distributes around the coast of Vietnam generally and Mekong Delta (MD) especially. However, this resource has not been utilized intensively in aquaculture in MD. The information on bioactivity of brown seaweed polysaccharde extrates and use of these extracts in aquaculture is limited. Therefore, the aims of this work are to examine the antioxidant activity of polysaccharide extracted from S. microcystum as well as its effect on growth performance of the white shrimp Litopenaeus vannamei.