Ac resistivity and power loss values for Mn-Zn ferrite material have been investigated by electrical and magnetic measurements. The ac resistivity shows an inductive dependency on frequency for the low dc resistive samples or for highly dc resistive ones at high temperature, while a capacitive dependency on frequency was observed for the highly resistive materials at the room temperature. These phenomena were interpreted by the dependence of ac resistivity on the dc resistivity, complex permeability and complex permittivity. The dependency of the power losses on the dc resistivity, temperature and frequence were also examined with analysis of power loss term. Dividing the power loss into hysteresis loss and eddy current loss, the frequency dependence of the eddy current loss was found to vary with the magnitude of the dc resistivity as follows: The eddy current loss of low dc resistive materials depends on the dc resistivity. On the other hand, the eddy current loss for high resistive materials is determined by the ac resistivity, contributed from dielectric loss.