Tungsten trioxide films were deposited on the glass substrate by electric current heating method using tungsten wire in air. Applied voltages to the tungsten wire were increased at rates of 0.05, 0.5, 5 and 50 V/min. The resultant films consisted of particles. A particle size of the crystals increased with increasing voltage applying rate. The effects of an ultraviolet (UV) irradiation on the reflectance of the films were investigated. The reflectance in the wavelength range of 500 - 2500 nm decreased by the irradiation. When the films were left in dark after the irradiation, the reflectance returned to the initial. With increasing voltage applying rate, absorption peak shifted toward longer wavelength in the region of 1250 - 1500 nm and the peak intensity decreased.