Al-doped zinc oxide (AZO) thin films have been prepared by spray pyrolysis (SP) technique of zinc acetate and aluminium nitrate, and the effect of thickness on structural and optical proper-ties has been investigated. The structural and optical characteristics of the AZO films were examined by X-ray diffraction (XRD) and double-beam spectrophotometry. These films, deposited on glass substrates at an optimal substrate temperature (T-S = 450 degrees C), have a polycrystalline texture with a hexagonal structure. Transmission measurements showed that for visible wavelengths. the AZO films have an average transmission of over 90%. The optical parameters have been calculated. The dependence of the refractive index. n, and extinction coefficient, k, on the wavelength for the sprayed films is also reported. Optical band gap of AZO is 3.30 and 3.55 eV. respectively. depending on the film thicknesses. (c) 2006 Elsevier B.V. All rights reserved.