Iron nitrides (FexNy) have attracted considerable attention as candidates for rare-earth-free hard magnetic material, and recently, the synthesis methods for FexNy nanoparticles have been established. Further, its magnetic properties might be useful for magnetic hyperthermia. Therefore, to assess its utility, the synthesis of FexNy nanoparticles was attempted in this study, and their magnetic properties and heat generation were compared with magnetite nanoparticles (MNPs), which have long been studied as biomaterials. Fe16N2 nanoparticles were successfully synthesized by reducing and nitriding MNPs with a size on the order of a few dozen nanometers, and the sample showed higher estimate heat generation than the MNPs. It was suggested that Fe16N2 nanoparticles might be used as thermal seeds for magnetic hyperthermia with higher heating efficiency.