Abstract:The extraction conditions of a new macromolecular polysaccharide from Lophatherum gracile Brongn.were optimized by single factor tests and response surface methodology.The thermal stability and antioxidant activity of the purified polysaccharide Lophatherum gracile Brongn.polysaccharide（LGP）were then determined.The extraction conditions were optimized as extraction with a liquid-to-solid ratio of 30 ∶1（mL/g）for 2 h and precipitation with 60% ethanol，under which the yield of crude polysaccharide from L.gracile reached（4.54±0.26）%.The purified polysaccharide，LGP，had an average molecular weight of 2.32×106 Da and the content of total sugar，protein，and glucuronide being（93.40±0.96）%，（1.71±0.64）%，and（5.50±0.78）%，respectively.LGP was mainly composed of rhamnose，arabinose，galactose，glucose，xylose，mannose，galacturonic acid，and glucuronic acid in a molar ratio of 0.115 ∶2.453 ∶3.176 ∶0.780 ∶1.000 ∶0.430 ∶0.239 ∶0.018.Furthermore，LGP was tested by a thermogravimetric analyzer and a differential scanning calorimeter.The results showed that LGP had good thermal stability below 200 ℃.In addition，LGP had the activities of scavenging DPPH·，·OH and ABTS+·and the reducing ability.In summary，LGP with good thermal stability and antioxidant property can be used as a new natural antioxidant，thus allowing the full utilization of L.gracile resources.