The zinc oxide thin films were deposited by the sol-gel method on the glass microscope slide substrates. The microstructure of films was determined as a function of film thickness as well as annealing temperature using X-ray line broadening technique and applying whole powder pattern modeling (WPPM). This investigation showed that the film thickness has no significant effect on the grain size, whereas the dislocation density decreases with the film thickness. On the other hand with the rise of annealing temperature the dislocation density decreases, but the crystallite size becomes larger. (C) 2010 Elsevier B.V. All rights reserved.