Based on the previous work (Yun et al., Chem. Eng. Sci. 59 (2004) 449-457), after the analysis of adsorbent structure, bed expansion and in-bed fluid hydrodynamics, a model was developed to describe the axial variations of the mean particle size and local bed voidage for adsorbents with a broad size distribution and different densities in expanded bed. In the model, the different-size particles were assumed to have different densities while the equal-size particles have the same density. Particle densities were described by a function that considered two parts of each particle: the resin-core part consisting of resin and inert core-particulates, and the thin resin film part without inert core-particulates. With UpFront FastLine SP adsorbents as interest test particles, the particle size and local voidage changes with bed height were measured in a 20mm I.D. column and then predicted by the model. It was shown that the mean particle size decreased, while the local bed voidage increased with increase of bed height. These trends are similar to those for particles with a broad normal size distribution and nearly uniform density. More obvious increase trends of voidage with increase of bed height exist in expanded beds with UpFront FastLine SP particles compared with those of Streamline particles. The present model gave a good prediction of bed expansion, the mean particle sizes and local voidages in most parts of bed compared with experimental data. (C) 2004 Elsevier Ltd. All rights reserved.