The electrophoretic deposition method is very useful for the coatings of metallic and nonmetallic materials which are impossible to be electroplated. Electrophoretic deposition of aluminum powder on steel plate has been reported in our previous papers, and in this paper the mechanism of this coatings has been studied. The solution employed was composed of 99.5% ethylalcohol and 0.4% water, and the bath temperature was kept at 20°C. Mild steel plate was used as cathode and carbon plate as anode. The electrophoretic deposition was done at the bath voltages such as 80, 160, 300 volt. The influence of the concentration of various additional electrolytes such as HCl, MgCl2, AlCl3 and SnCl4 on the amount of the powder deposits, the minimum bath voltage for deposition and the electrophoretic mobility of the aluminum particles have been examined. Moreover, the time dependencies of the amount of the powder deposits and the cathode current density have been measured, and the following conclusions were deduced from the results of these experiments: the factors affecting the amount of powder deposits are the repulsive force among the aluminum particles and the zeta potential of the surface of the alumiunm particles, hence the deposition of aluminum powder can occur when the electrophoretic force given by the electric field is stronger than the repulsive force among aluminum particles or the surface charge of the aluminum particles is canceled. The products on the cathode plate were not essential for the electrophoretic deposition.