Ultrasonic technique offers a good potential for phase holdup measurements in multiphase systems. Experiments were performed in an expanded fluidized bed consisting of water, air bubbles and/or glass beads. In this research note, the instantaneous signals of ultrasound were, for the first time, analyzed for the purpose of phase holdup determination. The results show that the fluctuations of the speed and attenuation of ultrasound are a well-defined function of solid and gas holdups in a multiphase system.