The saturation magnetization Ms of polycrystalline iron thin films increased by approximately 10% after the films were treated by ion nitriding for about one hour. In the nitride treatment, we used the magnetron discharge method to increase the energy density of the discharge. The rate of increase in Ms was 21.2% after the iron thin film was nitrided under an NZg as pressure of 4.5 × 10-2 Torr. Fe16N2, γ'-Fe4N, ε-Fe3N, ξ-Fe2N, and α-Fe phases were detected by the X-ray diffraction method in nitrided thin films under various N2 gas pressures. The saturation magnetization Ms of Fe16N2, calculated by using X-ray integrated intensity ratios, was 2210 emu/cc in the nitrided thin film under an N2 gas pressure of 4.5 × 10-2 Torr, and the Ms of Fe16N2, calculated by using X-ray integrated intensity ratios, was 1710 emu/cc in the nitrided thin film under an NZ gas pressure of 7.5 × l0-2 Torr.