The electrophoretic behavior of a concentrated dispersion of soft spherical particles is investigated theoretically, taking the effects of double-layer over-lapping and double-layer polarization into account. Here, a particle comprises a rigid core and an ion-penetrable layer containing fixed char-e. which ninnies biocolloids and particles covered by artificial membrane layers. A cell model is adopted to Simulate the system Under consideration. and a pseudo-spectral method based on Chebyshev polynomials is chosen for the resolution of the governing electrokinetic equations. The influence of the key parameters, including the thickness of the double layer, the concentration of particles, the Surface potential of the rigid core of a particle, and the thickness. the amount of fixed charge, and the friction coefficient of the membrane layer of a particle on the electrophoretic behavior of the system under consideration is discussed. We show that while the result for the case of a dispersion containing rigid particles can be recovered as the hunting case of a dispersion containing soft particles, qualitative behaviors that are not present in the former are observed in the latter. (C) 2004 Elsevier Inc. All rights reserved.