The purpose of this work is to study the nitridation behavior of Fe-Al base ternary alloys (containing Fe-28Al-2Mo and Fe-28Al-2Cr) over the temperature range 500℃~700℃ in aH2/NH3/Ar gas mixture. The nitridation kinetics followed the parabolic rate law, and the nitridation rates of the alloys were strongly dependent on ternary elements. Because the atomic radius of Mois higher than that of Cr, the Mo-content alloy has a larger lattice constant as Mo replaced thesubstitional site of Fe atom, which resulted in increasing N solubility, thereby increasing nitridation rates. The nitrides formed on Fe-Al base ternary alloys consisted of mostly Fe4N, Fe3N, and minor AlN. There is no evidence to reveal the formation of Mo or Cr nitrides.