ZnO:Al thin film was prepared using spin coating technique. After the coating process the texure of ZnO:Al film was exposed to Sr-90 radioisotope with 2.86 mCi. It was found that the texure of the film can be affected with beta radiation. The optical characteristics are critical at the end of the irradiaition process due to the charge trapping of radiolytic electrons or holes and the formation of defect centers and radiolytic electrons or holes using Sr-90 is. Beta radiation at ZnO:Al film led to a change in the physical properties such as colour when the beta radiation penetrated into the film. The evaluation of colour changes of irradiated ZnO:Al film is possible using the colour system. The dominant wavelength, brightness and excitation purity of ZnO:Al transparent film were evaluated. Colour co-ordinates were used for the determination of dominant wavelength and excitation purity of ZnO:Al thin film in the CIE tristimulus system.