Abstract: Effects of ultrasonic power,solid:liquid ratio and application time on the polysaccharide extraction from pitaya flowers were studied.Optimal processing conditions were determined using single factor and orthogonal experiments.They included the ultrasonic power of 180 W,a solid:liquid ratio of 1∶55,and a treatment time of50 min.The resultant yields of polysaccharide were found to be 68.49mg·g-1and 71.23mg·g-1 for Baiyu and Hongxin pitaya,respectively,with a significant difference(P<0.05)between the two varieties.The in vitro antioxidant activities measured by the total antioxidant capacity and hydroxyl radical scavenging ability of the extracted polysaccharides were high,particularly from Baiyu.The activities increased with increasing concentration of the polysaccharides,and a linear correlation between them on the extract from Hongxin pitaya flowers was found.