Abstract: The technological parameters of ultrasound-assisted extraction of polysaccharides from oriental tobacco buds were optimized with orthogonal test.The crude polysaccharide product was fractionated and purified with a sepharose CL-6B chromatographic column and two polysaccharide fractions(Fr-I and Fr-II) were obtained.The chemical compositions,structural characters and thermal stabilities of Fr-I and Fr-II were analyzed by GC,FT-IR and TGA,and their abilities for scavenging hydroxyl radical and DPPH radical were also determined.The results showed that:1) The optimized conditions for extracting polysaccharides from oriental tobacco buds were ultrasound power 300 W,ratio of water to raw material 30:1(mL/g),extracting for 6 min at 70℃.The yield of polysaccharide extracted under above conditions was 2.62%.2) The molecular weights of Fr-I and Fr-II were 181.97 and 16.27 kDa,respectively.3) Both Fr-I and Fr-II were heteropolysaccharides,IR spectra revealed that they were of α-and β-configurations,respectively.4) TGA results indicated that the degradation temperatures(T_d) of Fr-I and Fr-II were 195.7 and 180.5℃,respectively.5) Both Fr-I and Fr-II possessed good abilities for scavenging hydroxyl radical and DPPH radical,and the antioxidative activity of Fr-II was higher than that of Fr-I.