Thin films of Cobalt doped cadmium oxide are deposited on a glass substrate by spray pyrolysis method. UV-Visible spectrophotometer was used in order to determine the absorbance spectrum in the range of wavelength (300-900) nm. Transmittance, reflectance, and optical conductivity are studied for various annealing temperature of Co:CdO thin films. These results are related inversely with the value of the energy gap. Dispersion parameters such as Ed, Eo, M-1, M-3, So, and ëo are evaluated according to the single-effective-oscillator model.