The influence of Y3+ ions on structural and dielectric properties of nickel ferrites (NiFe2-xYxO4, where 0 <= x <= 0.3) has been studied. The as-synthesized samples, prepared by the co-precipitation method, were analyzed by XRD and FTIR which suggested that Y3+ ions were incorporated into the crystal lattice for all the samples. However, the XRD analysis of the sintered samples showed that secondary phases appear in the samples with x > 0.07. The samples have densities greater than 90% TD and the SEM images showed that the grain size decreases with the addition of yttrium. Dielectric properties measured from 150 to 25 degrees C in the frequency range of 100 Hz-1 MHz showed that the addition of yttrium slightly increases the ac conductivity and decreases the tg delta therefore making the materials better suited for the use in microwave devices. (C) 2013 Elsevier Ltd. All rights reserved.