Nanocrystalline nickel aluminate was prepared by chemical co-precipitation, and nanoparticles having different particle size were obtained by annealing the precursor at different temperatures. The TG/DTA measurements showed thermal decomposition was a three-step process with crystallisation of the spinel phase started at a temperature 420 degrees C. The X-ray diffraction analysis confirmed that the specimen began to crystallise on annealing above 420 degrees C and became almost crystalline at about 900 degrees C. The particle sizes were calculated from XRD. Dielectric properties of nickel aluminate were studied as a function of the frequency of the applied ac signal at different temperatures. It was seen the real dielectric constant epsilon', and dielectric loss tan delta decreased with frequency of applied field while the ac conductivity increased as the frequency of the applied field increased. The dielectric relaxation mechanism is explained by considering nanostructured NiAl2O4 as a carrier-dominated dielectric with high density of hopping charge carriers. The variation of e' with different particle size depends on several interfacial region parameters, which change with the average particle size. (c) 2005 Published by Elsevier B.V.