In this research, pure and copper doped cadmium oxide thin films were prepared by Successive Ionic Layer Adsorption and reaction (SILAR) method using cadmium acetate as the Cd source (cation) and hydrogen peroxide (anion). Optical transmittance is measured by UV–visible spectrophotometer, it is revealed that the copper doping and annealing at 300°C improves the transmittance of these films. The optical band gap of CdO increased to (2.8eV) with Cu doping, but it is decreased to (2.4eV) with annealing. The results show that the pure and doped CdO thin films at annealing temperature of 300°C have grain size in the range of 19.1nm and 44.4nm, respectively.