As a series of fundamental study on the gas evaporation method, a levitation-melted iron was evaporated in the gas mixtures of argon + ammonia, argon + nitrogen to synthesize ultrafine particles of iron nitride that got attention as one of the magnetic materials. The particles that were obtained in the gas mixture of argon and nitrogen were α-Fe. But nitrogen was chemisorbed on the surface of the particle, because nitrogen content in the particles was larger than the solubility of nitrogen in iron. The particles that formed in the mixed gas of argon and ammonia were Fe4N. The mean size of the particles of iron nitride was approximately 60 nm. The formation ratio of iron nitride was about 86 %.