It has long been recognized thatWO3can be colored through electro-, photo-, and thermo-chromism processes. We report here thatWO3turned to a deep blue color upon just one pulse irradiation of the XeCl excimer laser (&lgr;=308 nm, pulse duration=36 ns, output energy=100 mJ/pulse). Scanning electron microscopy (SEM) images showed that a melted layer was formed on the surface of the sample. The color change was demonstrated by UV-visible diffuse reflectance. X-ray photoelectron spectroscopy (XPS) showed the partial reduction ofWO3and the appearance of conduction band electrons. Calorimetry measurement results indicated that reoxidation happened at 400–440 °C in air. From these experimental results combining with the calculation, it was concluded that the laser-induced coloration is different from ordinary photochromism induced by UV light, and may be attributed to thermochromism. ©1997 American Institute of Physics.