Ultrasonic techniques were used to measure concentrations of solids and bubbles concentrations in two-and three-phase systems. The measurements have been made over a wide range of solid concentrations and gas holdups to characterize variations in ultrasonic signals in different regions. The solid phase used is 35 mu m glass particles while compressed air and tap water constitute the gas and liquid phase, respectively. The results show that in liquid-solid system both transmission time and amplitude ratio vary systematically with solids concentration. In presence of gas bubbles the variation of transmission time is not very regular while the relationship between attenuation of sound and phase hold-ups remained systematic.