Abstract—CuO nanoparticles were deposited by spray pyrolysis using aqueous cupric nitrate solution at substrate temperature 473K. The film grown at 473K showed a powder-like, non-oriented polycrystalline structure when they were converted afterwards to CuO by annealing. The X-ray diffraction pattern confirmed the formation of CuO nanoparticles. Transmission electron microscope analysis indicated that the as-synthesized particles are nanoparticles with an average particle size of 6nm. In addition to this, the ultraviolet-visible spectroscopy was employed to the resulting product to study its optical properties. Carbon dioxide gas sensing characteristics such as sensing response, operating temperature, transient response and stability was also reported.