The effects of ultrasonic vibration temperature on the microstructure of semisolid Sn-52Bi alloy and mechanical properties were investigated. The results show that the microstructure and mechanical properties are improved obviously after the ultrasonic treatment. Nearly round and uniformly distributed primary Sn phase particles were obtained under the cavitation and acoustic streaming caused by ultrasonic treatment. The best effects of ultrasonic treatment on microstructure and mechanical properties were obtained with the ultrasonic vibration for 120 s at 140℃. The elongation of semisolid Sn-52Bi alloy treated by ultrasonic vibration for 120 s at 140℃ was 42% and increased by 156.09% compared to conventional liquid casting Sn-52Bi alloy without ultrasonic vibration. It is a feasible and effective method to adopt the semisolid metal forming technology assisted with ultrasonic vibration to improve the ductility of Sn-Bi alloys.