Abstract: In order to investigate the structure and moisture retentivity of polysaccharides in fresh upper leaf of flue-cured tobacco, the polysaccharides in fresh upper leaves sampled from tobacco fields were extracted by alkali extraction method and purified. The monosaccharide composition was determined by HPLC, and functional group was characterized by FTIR. The molecular weight and conformation of the polysaccharides were determined by SEC/MALLS/RI, and the pyrolysis products and moisture retentivity were studied. The results showed that:1) The polysaccharides were composed of 42.91% glucuronic acid, 8.89% glucose, 32.31% mannose and 15.89% arabinose, and they were acidic β-pyranose. 2) The average molecular weight of tobacco polysaccharides was 6.587×10⁴, and the polydispersity coefficient MW/Mn was 1.557, and the α value for the double logarithm model of root mean square (RMS) radius of gyration was 0.279, which indicated that the molecular weight distribution of the polysaccharides was relatively homogeneous with spherical and highly branched conformation in aqueous solution. 3) The numbers of pyrolysis products of polysaccharides were identified to be 17 and 21 at 600℃ and 900℃, respectively. 4) The polysaccharides in tobacco leaf had a certain moisture retentivity, however their retention effect was lower than that of propylene glycol.