Artemisia selengensis Turcz (AST) is a perennial herb with therapeutic and economic applications in China. The effects of ultrasound-assisted extraction (UAE) parameters upon extraction yield (EY%), antioxidant and antitumor activities of the polysaccharides extracts were studied by using a factorial design and response surface methodology. The optimal conditions determined were as: ultrasonic power 146 W, extraction time 14.5 min. and extraction temperature 60°C. The average molecular weights of two homogeneous polysaccharides (APS1 and APS2) purified by DEAE cellulose-52 and Sephadex G-100 column chromatography were 125.4 and 184.1 kDa, respectively. Monosaccharide analysis showed that APS1 and APS2 were composed of five common monomers i.e., galactose, mannose, arabinose, xylose and rhamnose and one different monomer glucose and galacturonic acid respectively, with a most abundant part in molar % of APS1 and APS2 were glucose (83.01 %) and galacturonic acid (48.87 %) while least were xylose (0.80 %) and mannose (1.73 %) respectively. The antioxidant properties were determined by evaluating DPPH, hydroxyl radical scavenging activity and reducing power which indicated both APS1 and APS2 showed strong scavenging activities and anticancer activities on HT-29, BGC823 and antitumor activity on HepG-2. As UAE improved the polysaccharides yield than CSE, meanwhile, no significant difference of polysaccharides chemical compositions. Therefore, the present study suggests that the consumption of AST leaves may beneficial for the treatment of many diseases.