The ζ potentials of paint particles and the electrode potentials in the process of electrophoretic coating were determined and the mechanism of electrodeposition was elucidated by examining the relations between the both potentials. The ζ potentials were obtained from the electrophoretic velocity of the particles in a constant electric field, assuming that Helmholtz-Smoluchowski's equation would be applicable to spherical particles. While, the electrode potentials were measured on Pt, Ni, and Fe anodes, each having the area of 7.85×10-3cm2, under the conditions of being anodically polarized and painted with constant current. Furthermore, the curves representing the relations of potential-time and potential-current were discussed and the effects concentration of the paint solution on the latter curve was examined.As the results, it was suggested that the electrophoretic deposition of the paint particles would be accelerated by the diffusion layer formed by anodic reaction on the electrode. The diffusion layer would probably consist of oxide of anode metal and or hydrogen ion adsorbed. Although electrophoretic coating is usually applied to primary coating, the deposited paint film on the electrode does not always serve as an insulator. However, it would be probable to apply the electrophoretic coating to finishing in thick layer. However, there may be some disadvantage in the above application for practical use due to the properties of paint itself, with which this study is not concerned.