The influence of small substitution of iron with rare-earth cations in nickel zinc ferrites has been investigated. Samples with overall composition Ni0.50Zn0.51Fe1.96R0.04O4+δ (R = Pr, Nd, Eu, Ho, Tm, Lu) were prepared by a wet chemical route. The substitution of iron by rare-earth cations results in the formation of various rare-earth iron oxides in the bulk ferrite during sintering. Differences in the electrical and magnetic properties of the doped samples are interpreted on the basis of phase composition and microstructure.