Thin films of cobber doped ZnO have been prepared on glass substrate using the Sol–Gel spin coating technique. The effect of doping percentage of Cu to ZnO thin films on the optical properties and optical constants are concluded from absorption and transmission measurements, which are obtained by using double beam UV-Visible 1800 spectrophotometer in the wavelength (300-800)nm. It was found that the transmittance increases with increasing the doping percentage (0.01, 0.02, 0.03 and 0.04)mol%, while the Absorbance is decreased. The optical energy band gaps have been evaluated and their values seem to be decreased by increasing the doping concentration level in the range(0.01, 0.02, 0.03)mol% followed by a rise with in-creasing the doping level to 0.04mol%.