To　improve　the　electrochromic　properties　of　WO3　thin　films,　polyethylene　glycol　(PEG)-modified　WO3　films　via　Sol-Gel　method　were　prepared　on　indium-tin　oxide　(ITO)　glass　using　dipping-coating　technique　with　post　annealing　treatment　in　air.　Crystal　structures　and　morphologies　of　the　as-prepared　films　were　investigated　by　means　of　X-ray　diffraction　(XRD)　and　scanning　electron　microscope　(SEM).　Optical　properties　and　cyclic　voltage-current　characteristic　of　the　films　were　experimentally　studied.　Compared　with　the　corresponding　neat　WO3　films,　the　PEG-modified　WO3　films　exhibit　superior　electrochromic　properties,　which　possesses　longer　lifetime　after　5000　cycles　without　obvious　degradation,　as　well　as　higher　optical　modulation　up　to　71%　at　the　wavelength　of　633　nm.　The　results　suggest　that　PEG　addition　in　conjunction　with　post　annealing　treatment　may　change　the　micro-structure　of　WO3　films　to　increase　the　electrochromic　properties,　due　to　the　enhancement　of　ion　diffusion　capacity　in　the　electrochromic　material,　as　evident　from　the　formation　of　the　porous　structure　with　an　average　pore　diameter　of　9　nm.　As　cycling　stability　is　very　crucial　for　practical　applications　of　electrochromic　materials,　particularly　for　smart　windows,　this　research　provides　a　promising　low-cost　wet-chemical　route　to　high　performance　WO3-based　electrochromic　devices.