Ag-doped WO3 nanowhiskers have been successfully synthesized by a simple sol-gel treatment from the precursors W, H2O2, and AgNO3 at room temperature, followed by heat treatment at 400 degrees C for 1 h. The samples were characterized by X-ray diffraction (XRD), energy-dispersive spectrum (EDS), and scanning electron microscopy (SEM). Obtained results show that the obtained nanowhiskers width is ca. 200 nm with orthorhombic phase under different Ag-doped concentrations. Compared with the pure WO3-based sensor, all of the Ag-doped sensors showed better sensing performance in respect of sensitivity and selectivity. The sensor containing 3.0 mol % Ag exhibited the maximum sensitivity to formaldehyde vapor at 150 degrees C. A possible mechanism for the influence of Ag on the formaldehyde-sensing properties of Ag-doped WO3 sensors is proposed.