Abstract: Using Polygonatum sibiricum(PS)as raw material,ultrasound-assisted extraction was utilized to extract polysaccharides from Polygonatum sibiricum(PSP),then the polysaccharides were purified by DEAE-52 cellulose chromatography and Sephadex G-200,pure polysaccharides(PSP1-A)were obtained. Sulfated polysaccharides(SPSP1-A)was prepared by concentrated sulfuric acid method,and carboxymethylated polysaccharide(CPSP1-A)was prepared by sodium hydroxide-monochloroacetic acid system. Fourier transform infrared spectroscopy(FTIR)was used to verify the structure of the derivatives,and the antioxidant activity of PSP1-A before and after modification was compared by in vitro experiments. The results showed that the sulfated polysaccharides with a degree of substitution of 1.44 and the carboxymethylated polysaccharides with a degree of substitution of 0.49 were obtained. At the maximum concentration of 10 mg/mL,the scavenging rates of DPPH· and ·OH of CPSP1-A were 74.69% and 91.27%,respectively. Compared with the unmodified PSP1-A,CPSP1-A improved DPPH· and ·OH removal activity,enhanced reductive power,but reduced ABTS⁺ free radical scavenging activity while SPSP1-A enhanced scavenging effects on the above three free radicals,the scavenging rates of DPPH·,·OH and ABTS⁺· at 10 mg/mL were 98.70%,95.72% and 97.87%,respectively,and the reducing power was significantly improved,the SPSP1-A reducing power was more than three times that of PSP1-A at the concentration of 10 mg/mL. Both modifications were effective ways to improve the antioxidant capacity of PSP1-A.