The use of ultrasonic irradiation was proposed as a means to prevent scale deposition on a heat-transfer surface. A copper pipe was immersed in aqueous calcium sulfate solution, and the mass of calcium sulfate scale deposited on the pipe was measured. A significant amount of scale was deposited when ultrasonic irradiation was not applied, but no scale was deposited when it was applied. It was further found that intermittent irradiation during the period of scale nucleation was effective for the prevention of deposition.