The effects of ultrasonication on the hydrophobicity of oxidized pyrite and the flotation of an oxidized pyrite ore were investigated in this work. Surface examinations show that ultrasonication (≥ 0.3 W/cm 2 ) could result in surface cleaning and further oxidation of both slightly and heavily oxidized pyrite within 40 s. In the surface cleaning stage, the mechanical effects of ultrasonication removed the oxidation products from the pyrite surface. Further, in the surface oxidation stage, H 2 O 2 and oxygen formed by ultrasonication immediately oxidized the pyrite, leading to a notable decrease in the contact angle. It was found that the influence of ultrasonication is governed by the time rather than the intensity of ultrasonication. Ultrasonication significantly improved the recovery of pyrite in the rougher and cleaner stages, when ultrasound was used only during flotation. The unfavorable effects of ultrasonication, such as oxidation, were not notable during flotation of the pyrite ore, due to the weak ultrasonic field in the flotation cells and the limited flotation time. Additionally, ultrasonication favored the formation of fine bubbles in the flotation cell, which is also benefit for pyrite flotation. [ABSTRACT FROM AUTHOR]