The ferrite system Ni2Cu0.8-xZn0.2Fe2O4 with 0.0 <= x <= 0.8 was synthesized. XRD measurement confirmed the presence of single-phase spinel structure. The area ratio of Fe3+ at the tetrahedral A- and octahedral B-sites was deduced from the spectral analysis of Mossbauer measurements. The results give evidence that Ni2+ replaces Cu at B-site in the present unit cell. The dielectric properties epsilon', epsilon '', loss tangent tan(delta) and ac conductivity sigma(ac) have been studied for the prepared samples in the temperature range (300-600 K) and over the frequency range (10(2) to 10(5) Hz). The electrical conductivity results revealed a semiconductor behavior with increasing nickel concentration with a change in the slope at the transition temperature T-c. The variation of the dielectric parameters (epsilon', epsilon '' and tan(delta)) with frequency and temperature displayed a strong dependence on nickel concentration. Dielectric anomaly at the transition temperature T-c was pronounced in the relations of epsilon' and epsilon '' with temperature. The determined T-c was found to increase with increasing Ni content. The relation of tan(delta) with frequency at different temperatures showed two relaxation processes where the relaxation time and maximum frequency of the hopping conduction mechanism were determined. The results are explained in the light of cation-anion-cation and cation-cation interactions over the octahedral site in the spinel structure. (C) 2009 Elsevier Ltd. All rights reserved.