Cadmium sulfide (CdS) thin films with (111) preferential orientation were grown on glass substrates at room temperature by radio frequency (R.F.) magnetron sputtering. The structural and optical properties of CdS films have been investigated by X-ray diffraction, Scanning Electron Microscope micrographs, PL spectra and transmittance spectra. The grain sizes have been evaluated. The transmission spectra of the obtained films reveal a relatively high transmission coefficient (80%) in the visible range. All these results show that the grain sizes increased while the optical band gap decreased with increasing the thickness of CdS films.