The effect of Cr3+ ion substitution on the structural, magnetic and electric properties of Ni0.7Zn0.3CryFe2-yO4, where 0.0≤y≤1.0 is studied. All the investigated samples prepared by co-precipitation method and calcined at different temperatures. X-ray diffraction analysis for all samples show that, the nanoferrite samples are pure single phase spinel structure up to y=0.3. Both of the crystallite size and lattice parameter decrease with increasing Cr content. Discussion has been made on the basis of a comparison of the effect of the average crystallite size and Cr3+ ion concentration on the electrical and magnetic properties of Ni Zn ferrite.