Abstract: In order to improve the application value of polysaccharides from Chinese yam,the polysaccharides were extracted and isolated from the Chinese yam.Gas chromatography/mass spectrometry (GC/MS),fourier transform infrared spectroscopy,multi-angle laser light scattering (MALLS) and nuclear magnetic resonance (NMR) were used to characterize the structure of yam polysaccharides.Then,yam polysaccharides were sulfated by chlorosulfonic acid-pyridine method,and identified by FT-IR.Finally,the antioxidant activities of the polysaccharides and its derivatives were determined.The results showed that,the main monosaccharides in yam polysaccharides were 84.5% glucose,11.4% xylose,2.3% galactose and 1.4% arabinose.And the main structures were β-1,3-glucan and β-1,4-glucan.The content of α-glucan was low.The molecular weight of the yam polysaccharide was 6.6×10⁴ Da.However,the molecular weight of sulfated yam polysaccharide was lower than 1.0×10⁴.At the same mass concentrations,the antioxidant activities of sulfated yam polysaccharides were higher than that of yam polysaccharides.