In this research, cadmium oxide (CdO) nanoparticle thin films have been prepared at room temperature using a chemical bath deposition (CBD) technique, and the effect of the deposition time were studied. CdO thin films have been deposited on glass substrate from cadmium chloride (CdCl2) as cd +2 ions source and sodium hydroxide NaOH as O −2 ions source. The pH value (acidity level) of the chemical bath was fixed at about 11. The CdO thin films structures were analyzed by X-ray diffraction. It shows that all the prepared thin films have a cubic polycrystalline structure with a preferential orientation along (111) plane. All structural parameters were calculated. Particle size for the preferential orientation is calculated between (19.1-35.5 nm). It is found that the grain size increased with increasing the deposition time. UV-Vis spectrophotometer was used to study the optical properties, and a blue shift in the absorption peaks was noticed. The energy gap values (direct transition and indirect) calculated from the absorption spectrum located between (3.026-3.409 eV) for direct transitions and (2.197-2.917 eV) for indirect transitions, and this indicates that all CdO thin films prepared nanoparticles. We found that the energy gap decreased with increasing the deposition time.