The present study established the feasibility of a technique for monitoring FTJS lesion formation in vivo using localized harmonic motion (LHM) measurements. Oscillatory motion was generated within tissues by induction of a periodic radiation force with a focused ultrasound (FTJS) transducer. The harmonic motion was estimated using cross-correlation of RF ultrasonic signals acquired at different instances during the motion by using a co-focal diagnostic ultrasound transducer. The technique was evaluated in vivo rabbit muscle in an MR imager for simultaneous ultrasound harmonic motion tracking and MR thermometry. The calculated maximum amplitude of the induced harmonic motion before and after the lesion formation was significantly different for all the tested motion frequencies. During the FUS exposure a drop in the maximum amplitude value was observed and a threshold value could be associated to the formation of a thermal lesion. A series of controlled sonications was performed by stopping the exposure when the threshold value in LHM amplitude was reached and the apparition of a thermal lesion was confirmed by MR imaging.