The diffusion coefficient of a charged porous sphere is calculated numerically. The analysis is carried out under the Debye-Huckel approximation and the condition of equal ion diffusivity, yet can be applied to the case where the flow modification by the electrical body force is significant. As expected, the distortion of the charge cloud retards the movement of the particle. Our numerical results agree favorably with those based on a perturbation analysis for the case of very low electrical potential. When the particle charge is high enough, the electrical body force becomes increasingly strong to impede the fluid flow, thereby leading to a smaller resistance force compared to the perturbation result. (C) 2003 Elsevier Ltd. All rights reserved.