Tungsten oxide films were prepared by sol-gel and sputtering processes. The refractive indices and extinction coefficients of the films were calculated from the transmittance and reflectance spectra in the visible and infrared regions. The films were transparent in the visible and infrared regions when they were prepared by the 501-gel process and fired at 300°C and 500°C, and by the sputtering process under the conditions of O2/Ar=0.05 and 0.1 at room temperature. The refractive indices of the films depended on preparation conditions. The extinction coefficients of the films were almost zero in the visible and infrared regions. On the other hand, film prepared by the sputtering process under the condition of O2/Ar=0.01 was blue colored. The refractive index of the film increased with increasing wavelength in the visible and infrared region. The extinction coefficient ofthe film showed a large value at 1450 nm, which corresponds to the minimum of the transmittance spectrum of the film.