In this research we separated the exopolysaccharide from fermentation medium of Issatchenkia oriental by ethanol precipitation,and pure exopolysaccharide(EPS-I) was obtained by DEAE-cellulose52 chromatography after removing protein and dialyses.The structure of pure exopolysaccharide were determined by UV scanning.Identification of IR showed that the exopo-lysaccharide had polysaccharides specific function group such as —OH,—CH,—CO etc.but they were not proteoglycan.The hydrolyzate of pure exopolysaccharide was analyzed by Gas chromatography and the result indicated that the exopolysaccharide was mainly consisted of L-mannose,D-xylose and D-rhamnose,and their content were 3.62%,11.47% and 84.91%,respectively.Preliminary research on the antioxidant activity in vitro of EPS-I was done.Total antioxidant capacity(TAC),the scavenging rate of DPPH·,hydroxyl radical and superoxide anion were investigated in vitro.The results demonstrated that EPS-I had favorable antioxidant activity,at the concentration of 20mg/mL,the scavenging activities of DPPH· and O~-_2· radicals of EPS-I could reach to 80% above.