Novel room-temperature NH3 gas sensors based on Pd, tin oxide (SnO2) and reduced graphene oxide (RGO) ternary nanocomposite (Pd/SnO2/RGO) film were fabricated by the one-pot route. The Pd/SnO2/RGO ternary nanocomposite films were characterized by Fourier transform infrared spectroscopy (FTIR), Raman, X-ray diffractometry (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Microstructural observations revealed that the Pd and SnO2 nanoparticles easily and homogeneously attached to the surface of RGO. The sensor that was based on a Pd/SnO2/RGO ternary nanocomposite film responded strongly to low concentrations of NH3 gas at room-temperature. Its better sensor sensitivity than that of the pristine of SnO2 and SnO2/RGO nanocomposite film was related to the higher conductivity and catalytic activity of the Pd/SnO2/RGO ternary nanocomposite film.