As a result of advances in power electronics, in medium to high frequency high power conversion has become widespread. The performance and the sizing of the medium-frequency power transformer vary depending on material properties and operating frequency. While the core size determined by the power requirements, the specific core loss which varies depending on the frequency and the flux values becomes important. On the other hand, power handling capability of transformer varies according to the core material type and operation frequency. In this study, % 3 SiFe 0.1mm material was compared with the nanocrystalline material for the medium-frequency transformer cores. SiFe and nanocrystalline core materials are modeled, tested and analyzed for the different frequency values. Thus, the relationship between the frequency increase with the power handling capability and core losses were uncovered.