Abstarct: A water-soluble polysaccharide was isolated from the roots of Euphorbia seguieriana by water extraction at 75 ℃ and purified using chromatographic columns of Cellulose DEAE and Sephadex G-100. The homogeneity and molecular weight of purified polysaccharide were determined by using HPGPC. The especific optical rotation, monosaccharide composition, methylation, Periodate oxidation, Smith degradation, NMR and IR spectroscopy were used to determine polysaccharide structrure. The results showed that the polysaccharide of E. seguieriana roots was a galactoxyloglucan which composed of galactose, glucose and xylose in a molar ratio of 0.9, 8.2 and 0.1 respectively. The specific optical rotation and molccular weight of the purified polysaccharide were -35.9° and 13400 Da, respectively. The backbone of purified E. seguieriana roots was composed of →3) Glc (1→ and →3,6) Glc (1→, with branches attached to O-6 by β-D-Gal(1→ and →3) β-D-Xyl (1→.