CeO2 films is formed onto glass substrates by simple spray deposition technique using pyrolytic reaction of cerium nitrate hexahydrate which is termed as as-deposited film and the CeO2 film which is kept in furnace at 350 °C in the air atmosphere for 120 min is termed as heat treated film. The characteristics like structural, spectral, morphological and optical of both the films are studied. The structural analysis affirms that both the films are in cubic structure with polycrystalline nature. Uniform spherical shaped morphology is observed by SEM. The heat-treated film is chosen for the analysis of sensing characteristics for ammonia vapour with various concentrations (0.5–100 ppm) at room temperature. The better sensing performance with fast response and recovery times are achieved for 25 ppm of NH3. The room temperature response, fast transition time and perfect repeatability are achieved for low concentration (0.5 ppm) of NH3.