Improvement of proton conductivity of solid electrolyte films needs to form three-dimensional proton conduction paths by controlling the pore size and the pore structure between particles in particle films. A particle assemble method using electrophoretic deposition technique is useful for speedy and mass production assembly. In the electrophoretic deposition method, structure of particle array can be controlled by the electric field. As a result, the proton conductivity of the film showed a higher value for the regularly-arranged particle film and it is increased with a decrease in particle diameter. The proton conductivity of the film with the particles of diameter 50 nm had the highest value. The particle film with the well-controlled structure may enable the fuel cell to be operated in the middle temperature range. (C) 2011 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.