The electrophoretic mobility of a particle covered by a membrane in ana:belectrolyte solution is modeled theoretically. The membrane, which simulates the surface of a biological cell, is ion-penetrable, and carries homogeneously distributed negative fixed charges. An approximate expression for the electrophoretic mobility is derived. Based on the results of numerical simulation, we conclude the following: (1) The absolute Donnan potential increases with the concentration of the fixed chargesC0, but decreases with the ionic strengthI. (2) The greater the valence of cationa, the lower the absolute potential distribution. (3) The greater theC0, the greater the absolute mobility of a particle, |μ|, and the greater the friction coefficient of the membrane phase γ, the smaller the |μ|. (4) A largeIor a largealeads to a small |μ|. (5) The greater the ratio (permittivity of solution/permittivity of membrane phase), the smaller the |μ|. (6) For a large γ,|μ| decreases with the thickness of membranedunder the condition of constant amount of fixed charges. However, if γ is sufficiently small, the variation of |μ| as a function ofdexhibits a maximum. The classic result of Smoluchowski for the electrophoretic mobility of a rigid particle can be recovered as a limiting case of the present model.