Effect of Mn and Ni codoping on structure, optical and electrical properties of cobalt ferrite nanoparticles prepared by coprecipitation route have been investigated in detail. DSC-TGA, XRD and HRTEM studies have been explored to confirm the phase purity and structure. Most possible cation distribution as estimated by Rietveld analysis suggests the formation of mixed spinel ferrite phase by the migration of Co2+ ions from B site to A site and hence Fe3+ ions from A site to B site in different amounts due to the doping of Mn and Ni ions. UV-vis study reveals a red shift for Mn and Mn-Ni co-doped samples while a blue shift was observed in case of Ni doping. Conductivity spectra follows the double power law and the modulus spectroscopy study indicates the coexistence of two incomplete relaxation processes in the system that arises due to the co-contribution from both grain and grain boundary which were thoroughly confirmed by complex impedance analysis. Improvement in the dielectric properties in the materials due to doping could be beneficial for device applications. (C) 2015 Elsevier Ltd. All rights reserved.