This paper investigates the electrophoretic motion of a circular cylindrical particle with hemispherical ends in a circular cylindrical microchannel filled with an aqueous' electrolyte solution. The influences of three parameters on the electrophoretic motion of the particle are considered: the ratio of the particle radius to the channel radius, a/b; the ratio of the axial length of the particle to its radius, L/a; and the ratio of the zeta potential of the channel to that of the particle, y = zeta(w)/zeta(p). It is assumed that the electrical double layers are thin, that is, kappaa --> infinity. In the analysis, the liquid phase is divided into the inner region, which consists of the electrical double layers, and the outer region, which consists of the remainder of the liquid. A theoretical model governing the inner region and the outer region has been constructed, and a force balance on the particle surface is used to determine the particle velocity. The finite element method is employed to solve the resulting set of equations. It is found that the particle velocity in a microchannel decreases as a/b increases or as L/a increases. The particle velocity is also found to decrease linearly as y increases. On the basis of these results, an analysis of the electrophoretic separation of particles in a microchannel is presented. It is found that circular cylindrical particles of the same zeta potential, in small circular cylindrical microchannels filled with an aqueous electrolyte solution, can be separated by size.