Abstract: Objective To study the changes in antioxidant activity of rhodiola polysaccharide due to carboxymethylated modification.Methods Extraction of rhodiola polysaccharide was prepared with water extract-alcohol precipitation method.The conditions of carboxymethylated modification was optimized with orthogonal experiment.The elimination of 2,2'-azinobis-(3-ethylbenzthiazoline-6-sulphonate (ABTS)-related free radicals and superoxide anion free radicals were detected before and after the modification of rhodiola polysaccharide to evaluate its antioxidant activity.Results The optimal reaction temperature was 60 ℃ for the carboxymethylated modification of rhodiola polysaccharide under the chloroacetic acid dosage of 15 mg,the etherification reaction time of 3.5 hours,and the carboxymethyl substitution degree of 10.73.At the concentration of 5 mg/mL,the carboxymethylated rhodiola polysaccharide-induced scavenging of superoxide anion radical and ABTS-related free radicals were was 53.16% and 45.64%,which were obviously higher than the scavenging activities of rhodiola polysaccharide.Conclusion Rhodiola polysaccharide is of strong antioxidant activity after being carboxymethylated.