Abstract: The study aimed to optimize the cellulase extraction process of polysaccharide from Galla chinensis and study its antioxidant activity in vitro. On the basis of single factor test results, the Box-Behnken response surface methodology was used to optimize the extraction process of polysaccharide from Galla chinensis with the amount of enzyme, enzymolysis temperature, liquid-to-material ratio and enzymolysis time as the independent variables, and the yield of polysaccharide as the response value. DPPH free radical and hydroxyl radical scavenging rates were used to investigate the antioxidant activities of polysaccharides from Galla chinensis in vitro. The results showed that the optimal extraction conditions of polysaccharide from Galla chinensis by cellulase were as follows: enzyme dosage of 1.3%, enzymolysis temperature of 49℃, liquid-to-material ratio of 13∶1, enzymolysis time of 1.6 h and enzymolysis pH of 4.8. Under these conditions, the yield of polysaccharide from Galla chinensis was 4.27%, while the theoretical prediction value of regression model was 4.32%, and the error between the two conditions was less than 5%. The polysaccharide from Galla chinensis had strong scavenging effects on DPPH free radical and hydroxyl free radical, with the median inhibitory concentrations of 0.785 mg·mL⁻¹, and 1.173 mg·mL⁻¹, respectively. The cellulase enzymatic method could significantly improve the yield of polysaccharide from Galla chinensis. The process was simple and feasible, and the polysaccharide obtained from Galla chinensis has antioxidant activity in vitro.