Crude capsule polysaccharides( CCP) from S. zooepidemicus C55129 were separated by ethanol precipitation. CCP were separated and sequentially purified through a column of DEAE-cellulose 52 and a column of sephadex G-100 to afford purified fraction of capsule polysaccharide( PCP-I) with molecular weight of about 0. 0292 ×103k Da. The recovery rate of PCP-I was 5. 989 %. Monosaccharide composition and molar ratio of PCP-I were analyzed by Gas chromatography( GC). Results showed that arabinose ∶ mannose ∶ glucose ∶ galactose was 0. 99 ∶ 27. 03 ∶11. 84∶ 1. 00. In vitro antioxidant assay,PCP-I not only showed strong chelating ability for metal ions and inhibition of lipid peroxidation and reducing power,but also can moderately scavenge the activities of 1,1-diphenyl-2-picryldydrazyl radical,superoxide radical,and hydroxyl radical.