The physical properties of molybdenum oxide films for use in electrochromic display devices were investigated. This paper mainly concerns the dependence of the properties on the preparation conditions. The oxide films were prepared by thermal evaporation of MoO3 powder. The physical properties of the films depend heavily on the substrate temperature during deposition. The resistivity decreases with increasing substrate temperature, in the range 5 X 10(4)-1 X 10(10) Ohm cm. The optical bandgap and the refractive index of these films are 2.75-2.95 eV and 1.9-2.0, respectively. The structure of the films was examined by X-ray diffraction. The films prepared in the range 50-200 degrees C were amorphous, and the films formed in the range 320-400 degrees C were polycrystalline. The electrochemichromic properties of the films were also studied using asymmetric cells, and it was found that a good electrochromic performance was obtained for the films with similar to 1 X 10(10) Ohm cm.