Abstract: An objective is to provide a novel preparation method for a conductive ZnO film which realizes large area and mass productions with low costs and low environment loads. The crystal of zinc oxide (ZnO) is deposited on a substrate by a precipitation method using liquidous solution method under the presence of citric acid. The citric acid adsorbs on the surface of (0001) face of ZnO to suppress anisotropic growth to a c axis direction of the crystal in the precipitation reaction and to form dense crystal film on the surface of the substrate. Then, the organic acid incorporated in the film is photo-decomposed by irradiating UV light to the prepared ZnO crystalline film. As the result, carriers trapped by the organic acid is released to the crystalline film so as to provide an adequate conductivity.