Powder cores have the characteristic of low eddy current loss due to their high core resistance. The resistivity of powder cores can be controlled by modifying the insulating binder quantity, etc. On the other hand, hysteresis loss is mostly determined by the choice of the core material. Therefore, in order to make the most of the characteristics of powder cores, adjusting the core resistivity to the level where the eddy current loss is lower than the hysteresis loss for any given shape would be important. However, since eddy current loss largely depends on the core shape, it is not easy to determine the level of resistivity necessary.In this study, the authors investigated the correlation between the core loss and resistivity of small ring-shaped powder cores using a numerical modeling and compared the results with the experimental data.The calculation and experimental data showed a good agreement and the usefulness of this method was confirmed.The results suggest the possibility of application of this method to the larger and more complex shape cores.