The vacuum thermal evaporation technique created thin films of cadmium oxide nanoparticles at room temperature. The films were annealed at different temperatures (300, 350, and 425˚C) depending on the flow of oxygen. The XRD patterns of the nano-CdO thin film revealed that all of the prepared films have the (111) preferred orientation and an FCC structure with a cubic crystal structure. The optical properties of the thin films were studied and characterized using UV-Vis through an optical absorptiometry analysis, where the maximum absorption occurred at a wavelength close to 550 nm during annealing at 425°C with a high reflectivity of (0.016 - 0.2). The absorption coefficient increased as the annealing temperature increased, which led to direct transmission. The transmittance rises with the increasing wavelength for annealed and deposited films. The value of the energy gap was between 2.1 and 2.7 eV.