The high permeability Mn-Zn ferrites doped CaO-Bi₂O₃-MoO₃-xNb₂O₅(x= 0.000- 0.075wt%,step：0.015) were prepared by high temperature solid state reactions. The phase composition, microstructure and electrical and magnetic properties were measured by XRD, SEM, FPP, impedance analyzer and soft magnetic AC testing system. The effects of Nb₂O₅on the Microstructure and magnetic properties of Mn-Zn ferrites were investigated. The results showed that Nb₂O₅ can refine the microstructure, improve the density, frequency stability and quality factor, electrical resistivity and reduce specific losses when a small amount of doping Nb₂O₅ are added. Nb₂O₅ would result in the deterioration of microstructure and the electromagnetic properties of the Mn-Zn ferrites when a large amount of doping Nb₂O₅ is added. When the Nb₂O₅ doping amount is 0.030wt%, the best comprehensive performance of Mn-Zn ferrites were obtained.