ZnO thin films are deposited on glass substrates by using a sol-gel dip-coating technique with varying precursor concentrations. X-ray diffraction and field emission scanning electron microscopy analyses were used to investigate the effect of sol concentrations on the crystallinity and surface morphology of the films. The results show that with an increase in sol concentration, the value of the full-width at half-maximum of the (0 0 2) peak decreases while the strain initially decreases and then increases. Thin films deposited at high concentrations result in an increase in grain size. Studies of the optical properties of these films show that the band gap value varies between 3.266 and 3.281 eV when the sol concentration changes from 0.2 to 1.0 M, respectively. The 0.4 M ZnO thin films exhibited lower stress/strain than other films. It was determined that the properties of ZnO thin films are influenced by the stress and strain within the films. (C) 2012 Elsevier B. V. All rights reserved.