In order to improve the anticoagulant function of Auricularia auricula, Auricularia auricula polysaccharide(AAP)was converted into its derivatives by the microbial fermentation method and then polysaccharide derivatives with stronger anticoagulant activity were prepared. The optimal conditions for fermenting the polysaccharide from A. auricula were examined and the in vitro anticoagulant activities of transformed and untransformed polysaccharides were compared. Response surface tests and an orthogonal experiment indicated that the best conditions for microbial conversion of AAP3 were an AAP3 concentration of 4.0 mg/mL, a ratio of substrate(AAP3)to donor(p-hydroxybenzoic acid)of 40∶1, and a pH of 6.0. Bacillus subtilis Bs-07 was inoculated and then placed on a rotary shaker(120 r/min), followed by fermentation for 48 h at 35 ℃.The conversion rate was found to be greater than 40%. The result of in vitro anticoagulant activity showed that the transformed polysaccharide improved activated partial thromboplastin time, prothrombin time, and thrombin time values and greatly enhanced anticoagulant activity compared to the untransformed polysaccharide.