The present work investigates the polarization response in polycrystalline Ni0.9-yCuyZn0.1Fe1.98O4-delta (y = 0, 0.1, 0.2, 0.3, 0.4, 0.5) ferrite synthesized by solid-state reaction method. X-ray diffraction analysis confirmed cubic spinel phase formation in the calcined samples. Sintered samples contain a continuous network of CuO-rich segregation along the grain boundaries for y >= 0.2. Dielectric spectra showed a relaxation peak for y >= 0.2 in the frequency range of 1 kHz-1 MHz. This relaxation has been explained based on Maxwell-Wagner polarization considering two-layer model in connection with two heterogeneous dielectric media. (C) 2014 Elsevier B.V. All rights reserved.