Tungsten　oxide　(WO3)　films　were　prepared　on　indium-tin　oxide　(ITO)　glass　by　sol-gel　method.　The　influence　of　annealing　temperature　on　the　structural,　morphological,　optical,　electrochemical,　and　electrochromic　properties　has　been　investigated.　The　film　annealed　at　250　A　degrees　C　with　an　amorphous　structure　exhibits　a　noticeable　electrochromic　performance,　such　as　the　highest　optical　modulation　of　58.5　%　at　550　nm,　high　electrochemical　stability,　and　excellent　reversibility　(Q　(b)/Q　(c)　=　96.3　%).　An　electrochromic　(EC)　device　based　on　WO3/NiO　complementary　structure　shows　improved　performance.　It　exhibits　high　optical　transmittance　modulation　of　62　%　at　550　nm,　excellent　cycling　stability,　and　relatively　fast　electrochromic　response　time　(10　s　for　coloration　and　19　s　for　bleaching).