Abstract: A low rank coal possesses poor flotability due to its high hydrophilic character。A satisfactory result is difficult to achieve when using the tradition flotation method. Ultrasonic pretreatment on the low rank coal was carried out to enhance its flotation performance. The particle size analysis、contact angle analysis and infrared spectrum analysis was used to characterize the change of coal sample properties before and after ultrasonic treatment. The results indicated that the yield of clean coal increased by 5.41% while the ash content almost keep unchanged after ultrasonic pretreatment of 4min under the ultrasonic frequency of 20kHz and ultrasonic power of 135W. The particle size distribution of the coal sample changed significantly、contact angle increased and the amount of oxygen-containing functional groups decreased after ultrasonic pretreatment. Therefore, ultrasonic treatment can enhance the hydrophobicity of low rank coal and improve its flotation behavior dramatically.