This paper describes the use of an Electrical Capacitance Tomography (ECT) system for imaging a bubbling flow pattern within a fluidized bed. The raw data were processed using Matlab software to calculate average concentration values and AVS software was used to visualise the movement of a chain of bubbles through a fluidized bed. Quantitative data on bubble and slug sizes, bubble rise velocities, spacing and frequency was derived from the tomograms. The data concerned with solids concentration measurements obtained by the ECT system were compared with the measurements obtained from pressure transducers. The effect of several flow parameters as well as sensor geometry on measurement accuracy is discussed.