Effects of SnO2 addition on the structural, electrochemical, and electrochromic properties of WO3 electrodes were investigated, in which both the WO3 and SnO2-WO3 were synthesized via a sol-gel method. The SnO2-WO3 composite electrode, whose chemical states were identified through X-ray photoelectron spectroscopy analysis, gave the optical modulation of 38.3-99.5% and faster response times of 0.7 and 3.3 s. The coloration efficiencies of the SnO2-WO3 electrode were greater (49.7 cm(2) C-1) by 14% than the WO3 alone, together with the improved memory effect and durability during the electrochromic cycling tests up to 300 cycles. (c) 2007 The Electrochemical Society.