Thermal effects in the research of breaking kidney stones using HIFU-induced cavitation were studied. Damages to the phantom could be observed after an acting period of HIFU. It was shown that temperature rise is much greater in phantom than in water. Greatest changes occur near the focal region of HIFU transducer. Distinct temperature changes can be observed with input of continuous signals, while modest changes appear with input of pulsed signals. The fact that pulsed signals generate less damage, indicate the favourable acting patterns of HIFU. More tests are being done at the moment.