Abstract: In this research, polymeric prodelphinidins (PPs) were extracted and prepared from bayberry leaves and characterized using HPLC-DAD-ESIMS. Then effects of ultrasonic time, temperature, power and duty cycle on PPs were analyzed using one single factor test. On the above bases, the response surface methodology with Box-Behnken design was employed to study the ultrasonic conditions. Furthermore, the antioxidant capacity of PPs were determined before and after ultrasonic treatment by DPPH· and ABTS·⁺ methods. The results showed that yield of PPs from bayberry leaves was 5.96% (dry weight) with an average degree of polymerization of 27.8 and with a main structural component of EGCG. Ultrasonic treatments with different conditions had different influence on PPs degradation. Factors of ultrasonic time, temperature, power and duty cycle had significant effects (P<0.05). The optimized ultrasonic conditions were as follows: Ultrasonic time 74 min, temperature 44 ℃, ultrasonic power 361 W, and duty cycle 67%. Under these conditions, the yield of oligomeric prodelphinidins was 17.31%. After sonication, PPs possessed more significant antioxidant capacity than before (P<0.01).