Electrical resistance tomography (ERT) as an imaging technique was employed in this study for flow characterization, including simultaneous measurements of phase holdups and velocity distribution of individual phases in a gas-liquid-solid circulating fluidized Bed (GLSCFB). Application of ERT in three-phase flow systems is completely new. ERT is a non-invasive technique based on conductivity of the continuous phase, which provides color-coded cross-sectional view of the phases with a frequency of up to 250 Hz. The local conductivity measured by 16 electrodes located at the periphery of the plane inside the ERT measurement section, was then further converted into local phase concentration distribution based on Maxwell's relation. By cross-correlation analysis between the data obtained from both upstream and downstream planes, each consisting of eight electrodes, the phase propagation velocity was determined. Water was used as the continuous and conductive phase, while glass beads and air were non-conductive solid and gas phases, respectively. Qualitative and quantitative radial profiles of the phase holdup and propagation velocities were obtained. Phase holdup was also measured by pressure fluctuation, using online non-invasive pressure transducers and the results were in close agreement with the ERT results. Crown Copyright (C) 2007 Published by Elsevier Ltd. All rights reserved.