Response surface methodology( RSM) was used to optimize the ultrasonic extraction conditions of polysaccharides from Leucosceptrum canum Smith based on the Box-Behnken design. The factors of ultrasonic power,solid to liquid ratio,ultrasonic time were analyzed. The results showed that both ultrasonic power and extraction time had significant effects on polysaccharide yield. The optimum extraction conditions were as follows: ultrasonic power 548 W,ratio of solid to liquid 1∶ 30( g∶ m L),extraction time 55 min. Under the optimized conditions,the yield of polysaccharides was 17. 59%,which was closed to the predicted yield of 17. 74%.