Nitrogenation of Sm 2 Fe 17 powder was performed under a zero field and a magnetic field of 5 T at 623, 673 and 743 K to clarify the magnetic field effect on nitrogenation. Applying a magnetic field of 5 T induced nitrogenation compared with zero-field nitrogenation, and almost fully nitride Sm 2 Fe 17 N 2.9 was obtained at 743 K. Mössbauer spectroscopy results suggested that a 5-T magnetic field promoted the phase transformation to the fully-nitride Sm 2 Fe 17 N 3 phase. The magnetic field effect was discussed based on the magnetic energy gain and magnetic properties of host Sm 2 Fe 17 and fully nitride Sm 2 Fe 17 N 3 .