Nickel ferrite NiLayFe2-yO4 (0 <= y <= 0.05) was synthesized using citrate precursor method. The structure, particle size, shape and the homogeneity of the resulting nanoparticles were studied by X-ray diffraction and transmission electron microscope (TEM). IR was used to study the composition characteristics of the assynthesized sample. Magnetic susceptibility of the samples with different La contents was studied at different temperatures and magnetic field intensities. Ac conductivity, dielectric constant and loss tangent of ferrite polymer composites prepared with different ratios of 10%, 30% and 50% in polystyrene (PST) matrix have been investigated in the frequency range (10(2)-10(6) Hz). The dc magnetic susceptibility of the ferrite/PST matrix is also reported. (C) 2010 Elsevier B.V. All rights reserved.