This paper reports the effect of cobalt doping on ZnO thin films. Undoped and doped films were deposited on corning glass substrates by sol-gel method with different concentration of cobalt (0-10%). X-ray diffraction patterns show the polycrystalline nature of the films with the preferred orientation along c-axis. No other cobalt metal cluster and impurity phases have been observed with Co doping up to 5%. Raman spectra confirms the substitution of Co ion in place of Zn ion, however the films with Co concentration above 5% show peaks at 490 cm(-1), 525 cm(-1) and 715 cm(-1) which can be attributed to the formation of spinel ZnCo2O4 structure. Surface morphology and topography were studied using field emission scanning electron microscope and atomic force microscopy. The X-ray photoelectron spectroscopy results indicate that the Co ions are in + 2 charge state in the films. The optical transmittance of Co doped ZnO thin films reduces up to 80% as compared to undoped ZnO thin film in the visible region. The bandgap was found to be increasing in the range of 3.26-3.31 eV with Co doping whereas it decreases for higher doping of Co concentration. The M-H and M-T curve confirms the room temperature ferromagnetism in Co doped ZnO thin films. (C) 2016 Elsevier B.V. All rights reserved.