The optical properties of Zn_xCd_1-xS thin films were studied using the sputtering technique. The thickness of the film deposited at (50 degrees C) was around one micrometre. The optoelectronic transitions between valence and conduction bands were recognised by analysis of the absorption coefficient values within the fundamental absorption region. This test shows direct allowed transitions of (2.44 eV). The change in refractive index versus energy of the incident photon were calculated from the transmission spectrum. The study also shows the possibility of using such films as anti-reflection coatings when deposited on the surface of silicon solar cells.