Abstract: OBJECTIVE To optimize the extraction condition of the polysaccharides from Ephedra equisetina Bunge. and study its antioxidant activity in vitro. METHODS The polysaccharides were extracted from Ephedra equisetina Bunge. by hot water extraction. The single factor tests and response surface methodology were used to optimize the extraction condition. The antioxidant activity in vitro was evaluated by artificial free radicals in detail. RESULTS The optimum extraction condition was:extraction time 2.5 h, extraction temperature 73℃, ratio of liquid to material 25:1. Under the optimum condition, the yield was (5.57±0.072)%. The antioxidant activity in vitro showed that the polysaccharide from Ephedra equisetina Bunge. had a better scavenging effect on DPPH radical and hydroxyl radical with IC₅₀ of 703.9 μg·mL^-1 and 2 135.1 μg·mL^-1 respectively, and had a lower scavenging effect on superoxide anion radical and weak reductive effect on Fe³⁺. CONCLUSION The extraction condition is suitable to extract the polysaccharides from Ephedra equisetina Bunge. and the polysaccharide has certain antioxidant capacity in vitro but less than vitamin C.