One-pot polyol process was combined with the metal organic decomposition (MOD) method to fabricate a room-temperature NO2 gas sensor based on tungsten oxide and reduced graphene oxide (RGO/WO3) nanocomposite films. Fourier Transform infrared spectrometer (FTIR), X-ray diffractometry (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to analyze the microstructure and morphology of the fabricated films. The electrical and NO2 gas-sensing properties of WO3 to which various amounts of RGO were added were measured in detail as a function of concentration of NO2 gas at room temperature, to elucidate the contribution of RGO to the NO2 gas-sensing capacity. The NO2 gas-sensing mechanism of the RGO/WO3 nanocomposite films were explained by considering their composition and microstructures. The sensor that was based on a nanocomposite film of RGO/WO3 exhibited a strong response to low concentrations of NO2 gas at room temperature, satisfactory linearity and favorable long-term stability.