Electrochromic thin-film devices are in advanced stages of development for optical application. Films of Tungsten oxide were deposited in the vacuum chamber and were treated at different temperature. Properties of films were studied. The color of the fresh film is closely related with the substrate temperature, changing from colorless to light yellow and even to light blue when the temperature of the substrate increases. Infrared spectra results indicate that proton exists in the film as a form of O-H, and the strength of absorbed peak of active O-H at 3300 - 3450 cm -1 increases when the substrate temperature rises. Furthermore, it can be considered that the strength of peak of O-H vibration depends on the substrate temperature. No absorbed peak of H-O-H vibration appears. Measurement of visible spectra of the electrochromic film of a-WO3 was done for different conditions of electrochromic process. A special phenomenon was found, visible light transmittance of bleached film that remains the same in the electrochromic cycle is always different from the fresh film.