The electrochemical redox behaviors and electrochromic characteristics of tungsten trioxide (WO3) and Prussian Blue (PB) thin films have been examined in two- and three-electrode systems using polymer gel electrolyte (pge), which is based on composites of copolymer of 2-hydroxyethylmethacrylate and neopentylglycoldimethacrylate containing lithium perchlorate in the mixture solution of butylene carbonate and propylene carbonate. The conductivity of the pge prepared was ca. 10(-3) S cm(-1) at 30 degrees C. A reversible color change between blue and colorless was observed when an appropriate potential was applied repeatedly to the WO3- and PB-based electrochromic device (ecd). With the potential cycling more than 10(5) times less than 10% of the electrochromic characteristics were lost. The response time of the bleaching process of ecd using pge is higher than that using a solution electrolyte and the response time of coloration using pge is analogous to that using a solution electrolyte. The ecd properties characterized provide the optimum feature of the practical device.