An ultrasonic wave sound-pressure meassurement which uses a reference ultrasonic wave and a microparticle suspended liquid cell is proposed. In the method, microparticles are held in the liquid cell which is filled with the saline solution whose specific gravity is the same as the microparticles. If the cell is placed inside the standing wave which is produced by the ultrasonic wave to be measured and the reference ultrasonic wave, the microparticles are trapped in the standing wave and they are arranged at equal spaces. Then, the phase of the reference ultrasonic wave changes periodically; the microparticles reciprocate within the adequate range because the time-varying standing wave applies alternating acoustic radiation force to the microparticles. Since the displacement amplitude of the microparticle motion is proportional to the acoustic power, the sound pressure is estimated by measuring the displacement amplitude. In this method, the displacement amplitude is measured by observing the microparticles' loci when the cell is in the ultrasonic standing wave with adequate phase shift. Basic experiments are carried out by using polystyrene particles with a mean diameter of 40 (mu)m. Results almost agree with those measured by the hydrophone.