The aim of the present study is conducted to evaluate the antioxidant potential and toxicity effect of polysaccharide-fucoidan from the brown seaweed Sargassum tenerrimum. Fucoidan-a sulphated polysaccharide contains fucose and sulphate as major compounds. Interestingly, various studies reported that the presence of sulphate content of the sample plays a significant role in pharmacological activities. In this study, fucoidan was fractionated by Ion exchange chromatography method and it major chemical constituent sulphate and fucose was determined by the biochemical methods. The toxicity effect of fucoidan was analyzed by the brine shrimp toxicity assay. Three fucoidan fractions (F1, F2 and F3) were obtained from Intact Fucoidan (IF) through anion-exchange column chromatography. In vitro antioxidant capability was analyzed by 1, 1-diphenyl-2-picrylhydrazyl (DPPH), superoxide radical scavenging and total antioxidant assays and intact fucoidan showed the maximum activity 83.66 +/- 0.35, 81.73 +/- 0.35% and 41.6 +/- 0.43 mg g(-1), respectively. The finding of the present study was confirmed that the antioxidant property of fucoidan was depending upon the sulphate content of the fraction and these studies proved that fucoidan have non toxicity effect. Hence, fucoidan have the scope of being used as natural antioxidants in treating many human diseases.