The purpose of the present study was to enhance the classification performance of electrical field-flow fractionation (EFFF). In recent research by this group, the surface potential of silica particles treated with a bead mill displayed size dependency-smaller particles had a more negative zeta potential. This phenomenon and the EFFF system were used to classify the particles, with the bottom and top plates of the EFFF channel serving as negative and positive electrodes, respectively. In the present study, improvements to the EFFF channel were carried out to enhance classification accuracy. Walls of deionized water were utilized to prevent particles from contacting the electrodes. Because vertical electrophoresis led to the disturbance of particle trajectories in the channel by gravitational sedimentation, horizontal electrophoresis was applied. Furthermore, hydrodynamic force was induced in the channel creating differing linear velocities of the slurry and the water at the inlet. As a result, 200-nm particles could be classified at an applied voltage of 5 V with high accuracy when compared with the previous method that used vertical electrophoresis.