Various thickness of Zinc telluride (ZnTe) thin films were deposited onto glass substrates in terms of the thermal evaporation technique. The experiments XRD of both powder and thin films of ZnTe showed that the films are polycrystalline and have a zinc blende (cubic) structure. The effect of exposure to the oxygen plasma-immersion-ion-implantation (O− PIII) on the structural and optical constants of the same samples of different thicknesses were also investigated. It is observed that the oxygen PIII treatment can reduce both crystallite size and microstrain of ZnTe thin films. It is also observed that the oxygen PIII treatment can effectively improve the transmission spectra of the samples particularly in medium and transparent regions, therefore the refractive index decrease. The optical constants and energy gap of different thickness of ZnTe have been determined before and after oxygen plasma-immersion-ion-implantation (O− PIII). It is observed that the oxygen PIII treatment can effectively improve the transmission spectra of the samples particularly in medium and transparent regions, therefore the refractive index decrease. In addition, the optical band gap has been determined before and after O− PIII. The O− PIII causes an increase in the energy gap of different thickness of ZnTe thin films.