Abstract: Objective:Isolation and purified the polysaccharide from Ginkgo biloba leaf and investigated its structure characterization,antioxidant activity. Method:Extract polysaccharide from G. biloba leaf by ultrasonic assisted,crud polysaccharide was refined and then was isolated by anion exchange column,the relative molecular weight was measured by gel column chromatography,the monosaccharide composition was analyzed by GC,by adopting the method of in vitro antioxidant evaluation of G. biloba leaf polysaccharide antioxidant activity.Result : G. biloba leaf polysaccharide was purified and got three ingredients named GBLP Ⅰ, GBLP Ⅱ and GBLPⅢ. The relative molecular weight(Mw) was 41861,361352,637533 respectively. GBLPⅠwas consisted of rhamnose, arabia, mannose, glucose, galactose composition. GBLP Ⅱ and GBLP Ⅲ were consisted of rhamnose,arabia,mannose,galactose composition,but and the molar ratio was different. The result of antioxidant experiment in vitro showed that the ability of GBLP Ⅲ scavenging on hydroxyl free radical was strongest,followed by GBLPⅡ,GBLPⅠ,GBLP. While the ability of GBLPⅡand GBLPⅢ scavenging on superoxide anion was relatively good,followed by GBLP,GBLP Ⅰ. Conclusion:The monosaccharide composition and relative molecular mass of the fractions isolated from G. biloba leaf crude polysaccharide was difference. The ability of G. biloba leaf polysaccharide on hydroxyl free radical scavenging was stronger than the scavenging on superoxide anion,the hydroxyl free radical scavenging effect difference might be associated with Mw and structure.