The ferrites having general formula Ni 0.5−x Mg x−0.01 Zn 0.5−y Co y+0.01 Fe 2 O 4 (x=0.1, 0.2, 0.3, 0.4 and y=0.1, 0.2, 0.3, 0.4) were prepared by ceramic method. The X-ray diffraction studies of compositions reveal formation of single-phase cubic spinal structure. Dielectric properties such as dielectric constant ε′, dielectric loss tangent (tanδ), and ac resistivity were measured at room temperature as a function of frequency in the range from 1kHz to 1MHz. The plots of dielectric constant ε′ vs frequency show a normal dielectric behavior of spinel ferrites. The variation of loss tangent (tanδ) as a function of frequency shows a decreasing trend for all the samples except for the composition with x=0.3 and y=0.1, and y=0.2. The variation of ac resistivity with frequency of all the samples shows a decreasing trend with increase in frequency, a normal behavior of ferrites. All the variations are explained on the basis of Fe 2+ /Fe 3+ ion concentration on octahedral sites as well as the electronic hopping between Fe 2+ ↔Fe 3+ ions.