The present work reports the synthesis of undoped ZnO and Cr-doped ZnO nanomaterials by co-precipitation and hydrothermal methods. Crystallographic information of Cr-doped ZnO nanomaterials has been estimated by Rietveld analysis using MAUD. UV–visible absorption measurement concludes the significant reduction of band gap energy and the presence of strong s-d, p-d spin-exchange interaction in all co-precipitated nanoparticles as compared to the hydrothermally prepared rod-like structures. The dielectric response study of undoped and Cr-doped ZnO nanomaterials shows significant enhancement of the dielectric constant of the rod-like structures in comparison to the sphere-like nanoparticles. Impedance spectroscopy has been studied and the Nyquist plot or Cole-Cole plots of all the undoped and Cr-doped ZnO nanoparticles and nanorods have been constructed to understand the individual contributions of electrical responses of the grains and grain boundaries and the conducting nature of the nanomaterials.