A NO2 gas sensor based on mesoporous WO3 thin film with low operating temperatures and its sensing characteristics are reported. The mesoporous WO3 thin film exhibits regular pores with an average pore size of 5 nm and specific surface area of 151 m(2)/g. Excellent sensing properties are found upon exposure to 3 ppm of NO2 at 35-100degreesC for mesoporous WO3 thin film. The sensor response is 180 for 3 ppm NO2 at 100degreesC. The ability to sense NO2 at such low temperatures is attributed to the large surface area (151 m(2)/g) that offers many active sites for reaction with NO2 molecules. (C) 2003 The Electrochemical Society.