It was investigated that effect of suspension and electrolyte concentrations on zeta potential of alumini suspension and Iso-Electric Point(I.E.P.). The alumina powders in 0.1∼l $mu extrm{m}$ particle size distribution, and the electrolyte NH$_4$NO$_3$ were used for preparing the suspension and electrophoresis method was used for measuring zeta potential in this work. As the concentration of suspension was increased, zeta potential and the I.E.P. were increased, respectively. On the other hand, as the electrolyte concentration was increased, the I.E.P. was decreased. As a result of this work, the best condition for measuring zeta potential was the 0.01 wt% and 10 mM of the suspension and the electrolyte concentration, respectively.