Abstract: In order to optimize the technology for extracting polysaccharides from low grade tobacco and study their bioactivity, four factors, including ultrasonic power, extraction time, extraction temperature and solid/liquid ratio, were optimized with single factor test and L₉(3⁴) orthogonal test. The obtained crude polysaccharides were purified with a Sepharose CL-6B carboxymethyl agarose gel column, the scavenging activity of polysaccharides to free-radicals·OH and DPPH·was investigated, and the general antioxidant activity of polysaccharides was determined in vitro with ABTS method. The results showed that:1) The optimal conditions were:ultrasonic power 600 W, solid/liquid ratio 1:25, and extracting for 4 minutes at 60℃. Under such conditions, the yield of polysaccharides was 2.56%. 2) The obtained polysaccharides contained two fractions of different molecular weights. 3) The polysaccharides possessed strong in vitro antioxidant activity, obvious free-radical scavenging activity and potential nourishing and health care function. The results provided certain theoretical references for the utilization of low grade tobacco.