This paper investigates the electrical and magnetic properties of Cobalt-substituted Manganese-Zinc soft ferrite by the equivalent lumped elements acquired from the appropriate equivalent electrical circuit of polycrystalline ferrite. The equivalent lumped circuit, combined with equivalent lumped resistances and capacitance, is applied to investigate the effect of microstructure on electrical and magnetic properties of Cobalt-substituted Manganese-Zinc ferrites. Replacing a small portion of Fe2+ with Co2+ remarkably increases the bulk resistivity of the MnZn ferrite and decreases the core loss with lower eddy current loss. A longer isothermal duration causes grain growth and forms a larger equivalent capacitance, which conducts a drop of hysteresis loss. However, excess substitution of Co 2+ for Fe2+ is disadvantageous to magnetic permeability and raises core loss. The DC resistivity and magnetic permeability were measured by impedance analyzer at room temperature. The total loss of Mn 0.58Zn0.37Co0.01Fe2.04O4 ferrite core does not exceed 420 m W/cm3 at 300 kHz/70mT.