Polycrystalline tungsten oxide films with good electrochemical stability were prepared by dc reactive sputtering method. The Raman spectra of these films show that the W6+ ions were reduced to W5+ with the co-intercalation of Li+ ions and electrons. Intercalated electrons entered extended states of crystalline tungsten oxide and caused infrared reflectance variation, therefore, the emissivity of WO3/ITO/glass can be reversible modulated between 0.261 and 0.589. (C) 2002 Elsevier Science B.V. All rights reserved.