Abstract: In order to exploit resources of Sargassum fusiforme (Hary) Setch., the extraction and antioxidative activity of the polysaccharides from S. fusiforme ( SFPS) was investigated respectively. Based on single experiments, with yield of crude SFPS as index, extraction temperature, ultrasonic-irradiation time and ratio of liquid to solid were selected as factors, the extraction technology of the crude SFPS was optimized by quadratic regression rotatable orthogonal combinition design method. The results showed that the optimal extraction conditions were 87℃, 46∶1m L·g-1with 13 min. The corresponding extraction yield of crude SFPS was8.23%±0.01%. The sulfate-radical concentration of the crude SFPS was 10.93% ±0.24%. The SFPS content of the crude SFPS was 31.20% ±0.74%. The sulfate-radical concentration of the SFPS was 41.88% ±2.24%. The SFPS were sulfated. There was a linear positive correlation between the antioxidant ability of SFPS and the concentration in certain extent. The half-scavenging concentration IC50 values of the crude SFPS against ·OH, DPPH·, ABTS+· and O2-· radicals were 0.7068, 0.4814, 0.2527, 1.2350mg·m L-1respectively.