Electrochromic devices are based on the reversible insertion of guest atoms into the structure of the host solid. However, after cyclic operation, the tungsten in a WO3 film and the indium in an ITO (indium tin oxide) film were migrated with each other and the electrochromic property of the device was decreased. The trapped lithium is associated with the indium (diffuse out from ITO to WO, him). In order to block migration, a thin tungsten barrier film was deposited on the ITO film. With the tungsten barrier, the indium and tungsten migration was effectively blocked and the decrease of the maximum current of cyclic voltammogram was reduced to 1/10. We can now manufacture electrochromic devices that have long lifetimes and high transmittance variance.