Epitaxially grown Fe4N thin film on a MgO(001) substrate has been examined by high-field ferromagnetic resonance (FMR) spectroscopy. When the magnetic field was applied parallel (along the in-plane [100] direction) and perpendicular to the substrate, the resonance appeared at 2.4 and 4.9 T at 94 GHz, respectively. The g-value and the effective magnetization were estimated to be 2.13 and 191 emu g(-1), respectively, using the relation derived from the Landau-Lifshitz equation of motion. Superconducting quantum interference device (SQUID) measurements also showed that the Fe4N epitaxial film has a large magnetization anisotropy, supporting that the magnetic moments lie along the in-plane direction. (C) 2003 The Electrochemical Society.