A facile method for fabricating thin films of granular tungsten oxide (WO 3 ) particles decorated with nickel oxide (Ni 2 O 3 ) nanoparticles was developed for high response NH 3 gas sensor. The WO 3 granular film was fabricated by sputter deposition of tungsten, followed by oxidation. Ni 2 O 3 nanoparticles were deposited onto the WO 3 film by arc-discharge deposition of single-wall carbon nanotubes (SWCNTs) with Ni catalyst nanowires, followed by burning the carbon nanotubes. The Ni nanoparticle catalysts deposited on the SWCNTs were then oxidized to Ni 2 O 3 . The Ni 2 O 3 nanoparticles on the surface exhibited a catalytic role in ammonia gas reactions. A maximum response of 13.5 at operating temperature of 250°C to 200 ppm NH 3 gas concentration was found. In addition, the gas sensing mechanism of Ni 2 O 3 decorated WO 3 film was also discussed in this study.