To clarify the behavior of ZnO fine particles in an electric field in the presence of sodium hexamethaphosphate, we studied the effect of temperature, pH and concentration of electrolyte on the electrophoretic mobility and zeta potential of fine particles of different sizes. The absolute value of zeta potential of ZnO particles was found to be a maximum at pH 9 and to decrease in the high pH range, because the electric double layer is compressed by increasing NaOH concentration. Electrophoretic mobility was found to increase with increasing temperature, due to a decrease in viscosity of the solvent and the accompanying decrease in the resistance against the motion of particles. Electrophoretic mobility also decreased with decreasing particle size because of strongly acting asymmetric and electrophoretic effects. On the other hand, electrophoretic mobility decreased with increasing particle size above a critical value at which resistance due to viscosity is controlling.