The aim of this study was to improve the magnetic properties and reduce the core loss of a soft magnetic composite (SMC) core as the mixture of Fe-Si alloy and epoxy. In order to develop a soft magnetic core with high power driving characteristics, we investigated the magnetic and loss characteristics at different Si contents in the Fe–Si alloy-based SMC core. As the Si content was increased from 3.5 to 6.5 wt.%, the permeability and Q-factor of the core increased, and the core loss decreased. In particular, the Fe-6.5Si alloy–based SMC core containing 6.5 wt.% of Si showed the highest permeability of 23.27 H/m at 1 MHz as well as the largest Q-factor of 66.58 at the resonance frequency of 1.38 MHz. The Fe-6.5Si SMC core exhibited the lowest core loss of 693.94 mW/cm³ at 1 MHz. The findings of this study showed that the changes in the magnetic and electrical properties of the powder due to the addition of Si affects the magnetic permeability and core loss properties of the SMC core.