The crystal structure of manganese nitride material depends on the chemical composition. In this paper, we report the crystal structure of manganese nitride which depends on the deposition condition of a flow ratio of argon and nitrogen, F_N{=N₂/(Ar+N₂)}. The samples were fabricated by an RF-sputtering method. Argon and nitrogen were used as a reactive sputtering gas. The crystal structure of the obtained films was analyzed by X-ray diffraction (XRD) measurements. The stoichiometry of the film under F_N=5-100 % was evaluated as Mn₃N₂. The lattice spacing d of (101) expands as the nitrogen flow ratio increases. In the case of F_N=1 %, the composition was evaluated as Mn₄N. [DOI: 10.1380/ejssnt.2008.115]