Abstract: In order to study the structural characterization and antioxidant activities of fucoidan from Sargassum fusiforme, a heterogeneous polysaccharide SFP-2 was obtained by CaCl₂ solution extraction and anion-exchange. Structural characterization of SFP-2 was preliminarily determined by high performance gel permeation chromatography (HPGPC), chemical methods, high performance liquid chromatography (HPLC) as well as fourier-tansform infrared (IR). The antioxidant activities were evaluated by scavenging assays involving DPPH radical, superoxide anion, ABTS⁺ radical, nitrite and reducing power. Results indicated that SFP-2 appeared as a single and symmetrical peak in the HPGPC chromatogram and the average molecular weight was 707.0 kDa. The contents of total sugar, protein and sulfate ester were 66.9%, 3.1% and 21.2%, respectively. No uronic acid was detected, SFP-2 was mainly composed of fucose and galactose with a small amount of mannose and glucosamine. IR further proved SFP-2 was a sulfated polysaccharide. From the results, SFP-2 was a sulfated fucoidan without uronic acid. SFP-2 had good scavenging activity for DPPH radical, superoxide anio, ABTS⁺ radical and nitrite. The EC₅₀ values of the scavenging assays were 8.94, 8.30, 16.04, 9.87 mg/mL, respectively, with the ability of reducing power. Results above indicated that SFP-2 was a kind of non-glucuronic acid fucoidan which had better antioxidant activity.