Aluminum doped ZnO (AZO) thin films doped with different aluminum concentrations have been prepared by spray pyrolysis method onto glass substrates. The optical and structural properties of the films have been investigated by X-ray diffraction and optical characterization methods. The X-ray diffraction spectra showed that all of the thin films are of polycrystalline nature. The thin films have (002) as the preferred orientation. The optical band gaps of the films were calculated. The E (g) values decrease with increasing Al doping concentration. The refractive index, the extinction coefficient, and the real and imaginary components of dielectric constant are calculated. The obtained results show that all optical parameters keep constant in the visible region, whereas in the ultraviolet region, doping concentration strongly affects the optical parameters of AZO thin films. Optical constants tend to decrease with increasing doping concentration.