Eventhough Fe-6.5 wt.% Si alloy shows excellent magnetic properties, magnetic components made of the alloy with the composition are not totally commercialized because of its extremely low ductility. In order to overcome this demerit of alloy, 6.7 wt.% Si alloy powders were produced by gas atomization and then post-processed to form magnetic cores. By doing so, the total core loss could be minimized by reducing both hysteresis and eddy current loss, which were attributed to both grain size adjustment and particle size control. From our experiments, we were able to achive a core loss of 390 mW/cm3 at an induction of 0.1 T and 50 kHz through proper processes and a permeability μeff of 68 at low frequency was kept up to 700 kHz. These properties are compatable with the properties of well-known soft magnetic materials such as Fe-Si-Al and Ni- Fe alloys. From the above results, it can be concluded that Fe-Si alloy powders with high Si content have very high potential for the commercialization and application of the core.