The temperature rise of several kinds of bolt-clamped Langevin type vibrators which are used in the design of high power ultrasonic vibration equipment is measured as a function of operating time. Employing the wattmeter method and the variable mechanical load resistance proposed by the authors, the measurements are carried out for various values of the parameters of mechanical output power, mechanical load resistance and vibration velocity. The electroacoustic efficiencies of the vibrators are also measured using the same method.