Abstract: Hericium erinaceus(HE)was used as raw materials. Polysaccharides from Hericium erinaceus(HEP)was extracted by water. Acetylation of polysaccharides from Hericium erinaceus(A-HEP)were prepared.The degree of substitution was used as index,the effect of the ratio of polysaccharides to acetic anhydride(g/mL),reaction temperature and time on the degree of substitution of polysaccharide was studied. Based on single factor experiment,response surface experiments with Box-Behnken design for the optimization of acetylation process were adopted. Antioxidant activity of HEP and A-HEP was discussed.The optimal conditions of A-HEP were as follows:Material liquid ratio of 1:34 (g/mL),reaction time of 3 h and reaction temperature of 30 ℃.Under the optimum process conditions,the degree of A-HEP substitution was 0.609.Compared with the unmodified HEP,the oxidation resistances of A-HEP were improved. Acetylation modification was a method that could effectively improve the antioxidant activity of HEP.