Abstract: In order to study the antioxidant activities of fucoxanthin products extracted by supercritical carbon dioxide from Sargassum Fusiform, first, the experiments of reducing power, the clean-up rates on DPPH· and preventing effect on lipid peroxidation were performed using spectrophotometry and then the function of clean-up on ·OH, O-2·free radicals and H2O2 were studied by the method of chemiluminescence. Results indicated that fucoxanthin products of Sargassum Fusiform had doseresponse relationship with antioxidant activities, throwing a weak reducing power but strong clean-up rates on ·OH, O-2·free radicals, H2O2 and DPPH·. The IC50 for clean- up rates on ·OH was 386. 29μg/mL, superior to VC’s but below VE’s, the IC50 to DPPH· was 565. 2μg/mL, about 211. 4% of the VE’s and the IC50 to O-2· was 615. 71μg/mL, less than that of VE and VC. Preventing effect on lipid peroxidation was about 1/2 times of BHT and much more powerful than VC. Therefore, fucoxanthin products from Sargassum Fusiform had well antioxidant activities, and could be developed and used as native antioxidant hopefully.