A series of disposable gas-sensing paper-based film sensors were prepared rapidly by inkjet printing polyacrylic acid-coated silver nanoparticle (PAA/AgNP) ink onto the ordinary copy paper. The surface morphologies and chemical structures of the printed PAA/AgNP based sensing films with various thicknesses and spacing widths of interdigital electrodes were characterized. The electrical properties and the gas sensing performance of the film sensors were investigated and the results showed that the PAA/AgNP film sensors presented excellent selectivity, reproducibility and long-term stability to ammonia (NH3) gas at room temperature. The response of the PAA/AgNP film sensor to NH3 with the concentration of 25 ppm is 42.6% at 20℃ and 50% relative humidity (RH). The influences of thickness, spacing of interdigital electrodes and relative humidity on the sensing properties of the PAA/AgNP film sensors were also discussed and analyzed. Additionally, the PAA/AgNP film sensor presented perfect flexible stability and showed minor change in response value after 100 folding/extending cycles with the angle of 90°. In conclusion, the proposed high-performance paper based PAA/AgNP thin film sensor holds great promise for flexible, low-cost, portable, disposable and recyclable application in detecting NH3 at room temperature.