In the present work, the catalyst Pt was evaporated onto the sol-gel WO3, WO3-SiO2 films. These films were annealed at different temperatures and their structures were characterized by infrared, visible near infrared spectroscopy and X-ray diffraction. The coloring kinetics of the films was evaluated. The results revealed that the 0.75WO(3)-0.25SiO(2) composite films had faster coloring rates than the WO3 films. This improved behavior is attributed to the faster diffusion of atomic H resulting from the existence of more absorbed water, more pores, more phase boundaries, and more grain boundaries in the composite films. (C) 2002 Elsevier Science B.V. All rights reserved.