This work reports the enhancement of NO2 gas sensing response which owing to the incorporation of Ag nanoparticles into WO3 nanofiber matrices. Ag-doped WO3 nanofibers were fabricated by electrospinning. The Ag dopant levels ranged from 1 to 10 mol%. The microstructures and chemical compositions were examined using a series of material characterization methods including TEM, SEM, XRD, and XPS. Porous mats of nanofibers comprising monoclinic WO3 nanoparticles (28-39 nm) incorporated with small Ag particles were observed. The NO2 gas sensing performance was investigated at various gas concentrations (0.5-5 ppm) and operating temperatures (200-275 degrees C). For 5 ppm NO2 gas detection measured at 225 degrees C, the 3 mol% Ag-doped WO3 nanofiber gas sensor exhibited the highest gas response (R-g/R-a) of 90.3. This was approximately 9 times higher than that of the undoped sample. The response and recovery time were found to be in the range of 6-18 min. The response analysis obtained from CH4, NH3, SO2, H2S, and NO2 gas measurements suggests that the sensor has excellent selectivity toward NO2 gas. The improved gas response of Ag-doped WO3 nanofibers was attributed to both electronic and chemical sensitization mechanisms provided by Ag nanoparticles. Significant decreases in gas responses were observed in the samples with higher Ag dopant levels (5 and 10 mol%), where the crystallite size of Ag nanoparticles became too large and hindered their catalytic effects. (C) 2017 Elsevier B.V. All rights reserved.