Cobalt (Co) addition and thermal annealing induced structural and vibrational properties of ZnO nanostructures were analysed. X-ray diffraction pattern reveals that the nanostructures are in hexagonal wurtzite type and the formation of Co3O4. The Co ion induced morphology changes have been studied by high-resolution scanning electron microscope images and energy dispersive spectroscopy measurements confirm the presence of Co ions. CoO-related magnon excitation bands are emerged at room temperature for the Co-added samples. There are no changes in the band positions of the Raman spectra of pure and Co-added materials. Annealed sample exhibits the suppression of magnon bands and formation of Co3O4: ZnO composites. Raman line width and the electron phonon coupling constant are decreased with respect to the annealing temperature. The formation of Co3O4 : ZnO composite phases have further confirmed by infrared spectra. Copyright © 2013 John Wiley & Sons, Ltd.