This paper proposes a new estimation for the eddy-current loss of MnZn ferrite cores. The eddy-current loss plays a critical role in the frequency range of 100-500 kHz, whereas the amount of the hysteresis loss dominates the core loss of magnetic devices below 100 kHz. However, the definition and calculation of eddy-current loss are not as easy or accurate. In the proposed estimation, the equivalent electrical circuit method is conducted for determining the grain conductivity and the driving current to replace the induced magnetic flux density in order to simplify measurement. The related electrical and magnetic characteristics are measured by an HP-4294 impedance analyzer. Finally, an EI30 (PC40 material system from TDK) MnZn ferrite core is used as an example to prove that this model can effectively estimate the eddy-current loss of MnZn ferrite cores at different frequencies and driving currents.