Abstract: In the present study, the extraction process of polysaccharide from Bangia fusco-purpurea was optimized and the antioxidant activity of polysaccharide was studied in vitro. The effects of the extraction time, extraction temperature and ratio of material to liquid on the extraction amount of polysaccharide from B. fusco-purpurea were investigated, respectively, and the optimum preparation conditions were selected with orthogonal design combined with multi-index test. Meanwhile, the antioxidant activity of polysaccharide from B. fusco-purpurea was evaluated by DPPH free radical and hydroxyl radical scavenging method. The results showed that the optimum extraction conditions were the ratio of solid to liquid was 1∶40 (m/v) at 90℃ for 2.0 h. Under the optimum extraction conditions, the maximum extraction yield of polysaccharide reached (77.57±2.17) mg/g. Additionally, the result of antioxidant activity in vitro showed that the polysaccharide form B. fusco-purpurea presented significant scavenging effects on DPPH free radical and hydroxyl free radical. The IC50 value of DPPH free radicals scavenging was 0.36 mg/mL, and the IC50 value of hydroxyl free radicals scavenging was 0.65 mg/mL. This study can be used for the further development and application of B. fusco-purpurea polysaccharide.