The spinel ferrite system Ni1-xZnxLayFe2-yO4; 0.0 ≤ x ≤ 1.0 and y = 0.0, 0.05 is prepared by standard ceramic method. X-ray diffraction is used to obtain the structural characterization of Ni, Zn, Ni-Zn and Ni-Zn-La ferrite. The influence of zinc ion substitution on the electrical properties of samples is investigated indicating, that the ac conductivity (ln σ) as well as dielectric constant (ε') are nearly constant for small Zn ion concentration, while they increase at high Zn content (x = 0.6). The calculated values of the activation energy confirm the obtained results and indicate the semiconductor properties of the investigated samples. The dielectric constant data shows more than one peak which is discussed in view of the ionization potential of each element and hopping mechanism. © 2004 Elsevier B.V. All rights reserved.