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Background Nuoshanyao (NSY) is a special species of Chinese yam (Dioscorea opposita Thunb.) and shows rich functionality and superior nutritional value. The chemical components and structural properties of Nuoshanyao polysaccharide (NSYP) were investigated in his study. Results The molecular weight (Mw) of the major component in the polysaccharide was 23 kDa. NSYP was mainly composed of glucose, mannose, and galactose, and the molar ratio was 36.5:1.63:1. There might be an ordered helical conformation in NSYP, and the surface of NSYP was granular. NSYP exhibited strong scavenging capacity on the DPPH radical and chelating capacity on the ferrous ion in vitro with a rate of 94.94% and 82.49% at 4 mg/mL. Conclusion NSYP with the appropriate molecular weight range and helix structure could possess great antioxidant activity, while monosaccharide compositions may affect the activity. This work supplied important information for the potential application of NSYP in the nutritional and food industries.