Abstarct: A new water-soluble polysaccharide with molecular weight of 4.86 × 106 Da and a specific optical rotation of +31.5° (c 1.0, H2O), was isolated from the exudate gum of Amygdalus scoparia spach by extraction with hot water (75 °C) and purified by DEAE-cellulose A52 and Sephacryl S-400 HR columns, respectively . Total yields of crude and purified polysaccharides were 8.21% and 1.34 % respectively, and the total carbohydrate content of purified polysaccharides was about 97.6%, as determined by the phenol-sulfuric acid method. Monosaccharide composition analysis indicated that purified polysaccharides composed of Rha, Ara, Xyl, GlcA and Gal in a molar ratio of 1.0 : 20.3 : 4.9 : 3.1 : 17.8, and the uronic acid content of purified polysaccharide was about 6%. The structural feature of purified polysaccharides was investigated by a combination of optical rotation, partial acid hydrolysis, methylation analysis, periodic oxidation and smith degradation, Fourier transform-infrared spectroscopy (FT-IR), and nuclear magnetic resonance (NMR) spectroscopy. The results obtained from the analyses indicated that main water-soluble polysaccharide of exudate gum from Amygdalus scoparia was an highly branched arabinogalactan with a backbone consisting of (1→6)-lixnked β-D-Galp residues, (1→3)-lixnked β-D-Galp residues and (1→3)-lixnked α-L-Araf residues, and side chains β-D-Xylp-(1→3)-α-L-Araf-(1→3)-α-L-Araf-(1→), α-L-Rhap-(1→6)-β-D-Galp-(1→) and β-D-GlcAp-(1→6)-β-D-Galp-(1→) were attached to the backbone chain at O-3 and O-6 positions of 1,3,6-lixnked β-D-Galp residues.