A systematic technique has been developed to determine antiscaling efficiency and dissolution capacity for calcium carbonate in oilfield brines under various ultrasonic treating conditions. During the static experiments, effects of ultrasonic frequency, acoustic intensity, treating time, and water level on the antiscaling efficiency have been evaluated, while the underlying antiscaling mechanism is identified and determined. Physically, the formation of calcium carbonate is promoted as a result of the decreased molecular force and accelerated movement of salty ions under ultrasonic irradiation. Most of the formed scale is found to loosely suspend in the liquid, rather than tightly adhere to the solid surface. During the dynamic experiments, orthogonal tests have been designed to examine effects of interval time, treating time, and flow velocity on antiscaling efficiency. As for the dissolution experiment, dissolution capacity is measured to evaluate the effect of ultrasonic frequency on dissolution of the formed calcium carbonate. The antiscaling efficiency is found to achieve its maximum value of 81.1%, using the ultrasonic treatment with a frequency of 28 kHz, an acoustic intensity of 0.61 W/cm(2), an interval time of 2 h, a treatment time of 15 min, and a flow velocity of 1.8 m/s. It is also found that dissolution capacity does not impose a dominant effect on scale prevention and that the highest dissolution capacity of 19.3% is obtained with an ultrasonic frequency of 28 kHz.