We studied the electrophoretic migrations of submicron particles in nonpolar inks sealed in narrow gap cells of 5.3 mm by using optical and current responses. We evaluated the mobility of particles by using the optical responses of the total reflection at interfaces between electrodes and the solvent in addition to simultaneously measuring current, from which the concentrations of ions and charged particles were analyzed. The mobility of the particles in the narrow gap was similar to that of the bulk ink, except for the case with no charge director and less dependence on the charge director concentration. We also analyzed how the mobility was distributed and how the particles interacted with the interface by using the optical responses. #