Zinc oxide (ZnO) films have the potential in the emerging thin-film technologies which can be employed in thin-film solar cells, transistors, sensors and other optoelectronic devices. In this work, low cost sol-gel spin-coating technique was used to synthesize the ZnO films. The influences of annealing temperature on the structural and optical properties of ZnO and aluminum doped ZnO (AZO) films were investigated. The structural properties of the ZnO films such as surface morphology and crystallinity were determined using atomic force microscopy (AFM) and X-ray diffractometry (XRD), respectively. The optical properties of the ZnO films were characterized by the ultraviolet-visible (UV-vis) spectroscopy and Tauc method was adopted to estimate the optical gap. The experimental results reveal that the thermal annealing treatment affects the properties of the ZnO films. The effects of the low range annealing temperature on the sol-gel ZnO films addressed in this investigation will be discussed in this paper. (C) 2012 Elsevier B. V. All rights reserved.