Abstract: After fixing the ratio of basic raw materials of MnO, ZnO and Fe₂O₃, and then adding CaO with mass fractions of 0-1.0%, the Mn-Zn ferrite was prepared by traditional two-step synthesis process. The effect of CaO on microstructure and magnetic properties of Mn-Zn ferrite was studied. The results show that with increasing CaO addition content, the average grain size and sintering density of Mn-Zn ferrite increased first and then decreased; the elastic permeability at the frequency of 2.2 MHz increased first, then sharply decreased, and then slightly increased; the saturation magnetization at the magnetic field intensity of 1 T increased first and then decreased; the coercivity decreased first and then increased. Adding proper amount of CaO could improve microstructure of Mn-Zn ferrite and decrease core loss. When the content of CaO was 0.4wt%, the Mn-Zn ferrite had the largest saturation magnetization at the magnetic field intensity of 1T of 46 A·m²·kg^-1, the relatively large elastic permeability at the frequency of 2.2 MHz of 86.7, the relatively low loss power of about 20 kW·m^-3 and the relatively low coercivity of 183.4 kA·m^-1, and the Mn-Zn ferrite had the good comprehensive magnetic properties.