Properties of rf‐sputtered molybdenum oxide films for electrochromic display devices have been investigated. This report mainly concerns the dependence of the properties on the oxygen concentration in the sputtering atmosphere. The oxide films were prepared by rf sputtering from a compressed powder MoO3target under an operating pressure of 4×10−2Torr using a mixture of Ar‐0.5–50% O2. Electrical resistivity of the films formed increases with increasing oxygen concentration in the sputtering atmosphere and ranges from 2.5×1010to ∼1×1012&OHgr; cm. Spectral transmittance of the films is about 85% in the visible and near‐infrared region. Optical band gap and refractive index of these films are 2.67–2.76 eV and 2.01–2.26, respectively. Electrochemichromic properties of the films were also studied using asymmetric cells, and it was found that a good electrochromic performance was obtained usually by the cells composed of the films with a resistivity of 2.5×1010&OHgr; cm.