Polyol process was combined with metal organic decomposition (MOD) method to fabricate a room-temperature NO 2 gas sensor based on a tungsten oxide (WO 3 ) film and another a nanocomposite film of WO 3 /multi-walled carbon nanotubes (WO 3 /MWCNTs). X-ray diffractometry (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to analyze the structure and morphology of the fabricated films. Comparative gas sensing results indicated that the sensor that was based on the WO 3 /MWCNT nanocomposite film exhibited a much higher sensitivity than that based on a WO 3 film in detecting NO 2 gas at room temperature. Microstructural observations revealed that MWCNTs were embedded in the WO 3 matrix. Therefore, a model of potential barriers to electronic conduction in the composite material was used to suggest that the high sensitivity is associated with the stretching of the two depletion layers at the surface of the WO 3 film and at the interface of the WO 3 film and the MWCNTs when detected gases are adsorbed at room temperature. The sensor that is based on a nanocomposite film of WO 3 /MWCNT exhibited a strong response in detecting very low concentrations of NO 2 gas at room temperature and is practical because of the ease of its fabrication.