Understanding of the effects of the boundary - the channel walls - on the electrophoretic motion of particles in microchannels is very important. This paper developed an analytical solution of the electrophoretic mobility for eccentric motion of a rectangular particle in a rectangular microchannel. The simple geometry of the system does not limit the generality of the qualitative prediction of the model and the analytical solution. Several special cases are Studied, and the effects of the degree of the eccentricity, the particle's size relative to the channel's size, and the relative zeta potentials on the particle's mobility are discussed. For the case where the particle's cross-section area is close to the cross-section area of the microchannel, the model's predictions are compared with the published experimental results and good agreement was found. (C) 2009 Elsevier Inc. All rights reserved.