In this work, ZnO thin films with different thickness (100 nm and 50 nm) were deposited onto flexible-transparent substrates by high vacuum (HV) reactive direct current (DC) magnetron sputtering technique, using oxygen as a reactive gas. The structural and optical properties of the films were investigated by X-ray diffractometer (XRD), room temperature photoluminescence (PL) and UV–Vis spectrometer. The both obtained films had a hexagonal structure and a highly preferred orientation with the c-axis perpendicular to the substrate. The electronic transitions from the conduction band to the valence band (called as band gap) of the films was about 3.2 eV. It was observed that the exitonic transition energy of the films shifted blue emission with increasing the film thickness. In addition, the optical transmittances of the films were about 80 % in the visible region.