Using a vacuum dry process, we constructed an all-solid-state transmittance-type electrochromic (EC) device consisting of five thin layers: ITO/IrOx/Ta2O5/WO3/ITO. We measured the optical and electrochemical properties of the EC device. By using Ta2O5 film as a proton conducting solid electrolyte, the device exhibited a fast response speed of 0.2 s and stable coloration characteristics. With an AC impedance method, we determined the properties of the device under varying temperature and environmental conditions. In the solid electrolyte (Ta2O5), the ion resistance controlled the response speed; the ionic conductivity and activation energy were 3 x 10(-6) S/cm and 0.31 eV, respectively. (C) 2009 Elsevier B.V. All rights reserved.