Nanostructure ZnO and ZnO:Co films were deposited onto borofloat glass substrates by the sol-gel method using spin coating technique. X-ray diffraction (XRD) study was used to investigate the effects of cobalt dopant on the crystalline structure and orientation of the films. XRD observations showed that the crystalline quality of ZnO film decreased with increasing cobalt content. The effect of Co incorporation on the surface morphology was clearly observed from scanning electron microscopy (SEM) images. The chemical composition of the 3% Co doped nanostructure ZnO film was confirmed by X-ray photoelectron spectroscopy (XPS). The doping of ZnO with Co causes a decrease in particle size and crystallinity while it leads to an increase in the band gap, which changes in accordance with the Burstein-Moss effect. The optical constants of the films such as refractive index and extinction coefficient were determined using transmittance and reflectance spectra. The sheet resistance of the films, which was calculated using Van der Pauw method, first increased by about two orders of magnitude and then tended to decrease. (C) 2013 Elsevier B.V. All rights reserved.