Abstract: Acidic polysaccharide secreted by Aureobasidium pullulans was separated using cetyltrimethylammonium bromide ( CTAB) as precipitant and its solubility as well as antioxidant activity in vitro compared to pullulan were studied.The optimal conditions were obtained through single factor experiments and orthogonal experiments and they were as follows: the ratio of3% ( w/v) CTAB solution to initial polysaccharides solution was 1 ∶ 1, concentration of initial polysaccharides solution was7% ( w/v) , precipitation time was 12 h.Under this condition, the extraction rate of acidic polysaccharide was 5.01%.This kind of method kept structure integrity of acidic polysaccharide and pullulan and provide references for further research of this polysaccharide.Results of properties comparison between acidic polysaccharide and pullulan indicated that pullulan was easily soluble in water but acidic polysaccharide was only slightly soluble in water.The antioxidation activities of acidic polysaccharide and pullulan were similar when the concentration was in the range of 0 to 1 mg/m L. The reducing power, scavenging rate on superoxide radical and hydroxyl radical of this two kinds of polysaccharides increased with the increase of solution concentration. It could offer theoretical references for further development and application of acidic polysaccharide from A.pullulans.