Abstract: Using Aralia chinensis L.stem- bark as materials,optimal process conditions of ultrasonic- assisted extraction of Aralia chinensis L.stem- bark polysaccharides( ACSP) and its antioxidant activities were studied.According to the Box- Behnken design principle,based on the single factor experiment,four- factor( ratio of water to material,extraction temperature,ultrasonic power and extraction time) three- level response surface methodology( RSM) was conducted.The optimal extraction conditions of ACSP were determined as follows: ratio of water to material was 33 m L / g,extraction temperature was 71 ℃,ultrasonic power was 124 W,extraction time was93 min.Under optimal conditions,predicted value of polysaccharides yield was 12.897%,verified value was 12.871± 0.11%.The results of antioxidant activities of ACSP in vitro showed that the scavenging activity of DPPH,hydroxyl radical,superoxide radical and reducing power increased with the increase of polysaccharides concentration in the experimental range.Conclusion: the regression model generated from RSM was feasible to optimize the ultrasonicassisted extraction process of ACSP.ACSP has good antioxidant activity,which may be explored as a natural antioxidant in medicine or functional foods areas.