We observed proton transfer phenomenon Of WO3 in Au-WO3 nanocomposite thin-film electrode prepared by sputtering deposition method. The Au-WO3 nanocomposite electrode formed using both the An and WO3 targets consisted of a nano-sized An crystalline phases and a tungsten oxidative phase, indicating the formation of crystalline Au nanophases, as confirmed by X-ray diffraction analysis and X-ray photoelectron spectroscopy. In particular, due to An metallic nanophases, the modified electrochromic and electrochemical properties of WO3 were observed. The Au-WO3 electrode showed a reverse optical modulation with respect to applied potential compared to that Of WO3 electrode. (C) 2005 Elsevier Ltd. All rights reserved.