Abstarct: In this research a new water-soluble polysaccharide was extracted from the roots of Echinops Pungens by warm water (۷۰ C̊). The average molecular weight and specific optical rotation of this polysaccharide were ۶۵.۷ kDa and -۸۸.۲° respectively. Purification of the polysaccharide was done by DEAE-cellulose and sephadex G-۱۰۰ column chromatography. The results of gas chromatography was showed that monosaccharides of this polysaccharide were galactose (Gal), glucose (Glc), mannose (Man), xylose (Xyl) and arabinose (Ara) with a relative molar ratio of ۰.۹۶, ۵.۲۳, ۱.۰۰, ۲.۰۶ and ۱.۰۴ (about ۱:۵:۱:۲:۱) respectively. For structure identification of polysaccharide, different chemical and instrumental analysis such as FT-IR, partial acid hydrolysis, periodate oxidation and Smith degradation, methylation and NMR spectroscopy (۱D and ۲D) was used. Result showed that the main structure of this polysaccharide was composed of (۱→۶, ۱→۴,۶)- lixnked glucose residues, with branches at O-۴ position of some glucose residues, consisting of β-D-xylopyranose(۱→۴)-β-D-xylopyranose(۱→) and β-D-mannopyranose (۱→۴)-β-L-arabinopyranose (۱→۴)-α-D-Galactopyranose (۱→). Antioxidant activity of this polysaccharide, was recognize by scavenging activity in the DPPH radicals, showed that it was concentration-dependent manner and totally the antioxidant activity was not significant.