Oxygenated cadmium telluride (CdTe:O) thin films are prepared by radio-frequency (RF) sputtering from a polycrystalline CdTe target in an atmosphere composed of a mixture of argon, nitrogen and oxygen gases. X-ray diffraction analysis showed that as-deposited films are amorphous when deposited in the presence of nitrogen. X-ray photoelectron spectroscopy analysis revealed that the layers do not contain any nitrogen while the chemical composition of the films depends strongly on the partial pressure of N-2 used during sputtering. Finally, optical transmission measurements in the IR-Visible region showed that the optical constants of the samples vary considerably with their oxygen contents. X-ray reflectometry studies enabled us to correlate some of these variations with the density of the layers.