Ultraviolet (UV)-irradiated titanium dioxide (TiO2) photo-catalyst surfaces exhibit excellent oil repellency and therefore an oil droplet cannot adhere to its surface in water even when tightly pressed to it. Ultrasonic irradiation treatment in water greatly decreases the degree of underwater oleophobicity, allowing the oil droplet to adhere to the surface in water. We demonstrate that UV and ultrasonic irradiation treatment can be used to reversibly change the underwater oil repellency of TiO2 surfaces.