Abstarct: A new water-soluble polysaccharide with molecular weight of 82.4 kDa and a specific optical rotation of +19.5◦ was extracted from the roots of Echinops cephalotes DC by hot water extraction (80◦C). Purification of the polysaccharide was carried out by DEAE-cellulose and Sephadex G-100 column chromatography. The total suger content of purified polysaccharide was 96.9% and no protein and nucleic acid were detected in the polysaccharide. Monosaccharides analysis revealed that the purified polysaccharide of E. cephalotes DC roots was composed of Glucose, Arabinose, Xylose and Rhamnose with a relative molar ratio of 4.12, 98.0, 1.06 and 1.00 (4:1:1:1). Structure identification of polysaccharide was elucidated by a combination of methylation, partial acid hydrolysis, GC-MS analysis, periodate oxidation and smith degradation, FT-IR and NMR (1D and 2D) spectroscopy. The data obtained indicate that main chain consisted of (1→6, 1→4,6, 1→3,6)- lixnked β-D-glucopyranose residues, with branches at O-3 position of β-D-glucopyranose consisting of α-L-arabinoforanose (1→3) and β-D-xylopyranose (1→) and at O-4 position β-D-glucopyranose consisting of α-L-rhamnopyranose (1→). Antioxidant activity of this polysaccharide, was recognized by scavenging activity in the DPPH radicals, showed that it was concentration-dependent manner and was less than that of ascorbic acid at the same concentrations.