A numerical algorithm is developed to study the electrophoresis of polyions where account is taken of ionic relaxation. The algorithm involves simultaneous solution of the Navier-Stokes equation by a discretized integral equation method and of Poisson and ion-transport equations by the finite difference method. It is applied to the electrophoresis of spherical polyions containing centrosymmetric charges, and the resulting mobilities are in excellent agreement with those of Wiersema et al. (J. Colloid Interface Sci. 1966, 22, 78). The extent to which ion relaxation perturbs the charge density and velocity field around the polyion is investigated.