Electrophoresis in a concentrated suspension of charged porous spheres is investigated theoretically, taking into account of the polarization effect of double layer in particular. The double layer thickness and fixed charge density of the porous spheres are arbitrary and double layer overlapping is considered as well. A pseudo-spectral method based on Chebyshev polynomial is used to solve the resulted general electrokinetic equations. Local extrema are observed in the mobility profile as the double layer thickness varies, which is absent in previous theoretical studies neglecting polarization effect but agrees well with the experimental observations in the literature, indicating the importance of polarization effect in correctly interpreting the electrophoretic experimental results. A simple mutual transform of mobility predictions between Levine-Neale and Shilov-Zharkikh boundary conditions is established and confirmed by direct calculations, which facilitates the dialogue between theoretical and experimental researches. In general, the higher the fixed charge density, the more significant the polarization effect is. (C) 2008 Elsevier Ltd. All rights reserved.