Axial distribution of adsorbent particle as well as local voidage variation is very important and fundamental for the predicting and understanding of adsorptive performance in expanded bed adsorption. Based on the analysis of bed expansion and fluid hydrodynamic behaviors, a model was developed to predict the mean particle size and local voidage variations with the axial bed height under various operation conditions in expanded bed. Experimental measurements of particle size and local voidage changes with bed height were conducted in a modified glass column of 20 mm inner diameter with sampling ports. Experimental data obtained in this work and in the literature with Streamline SP, Streamline Phenyl and Streamline quartz base matrix particles in the columns of inner diameters 20 -50 mm, were used to verify the model prediction. The results were in good agreement with the experimental data. (C) 2003 Elsevier Ltd. All rights reserved.