Composite diffusive nitrided layers with precipitates of iron phosphides are considered. They are generated in the process of nitriding in an atmosphere of partly dissociated ammonia with a slight admixture of gaseous phosphorus. The addition of small quantities of gaseous phosphorus to the nitriding atmosphere influences the structure and properties of the nitrided layer. The layers consists of: a zone of phosphides of Fe 3 P and Fe 2 P, a zone of nitrides of Fe 2–3 N and Fe 4 N, and a zone of precipitates of iron phosphide Fe 3 P in the zone of nitrides of Fe 2–3 N and Fe 4 N. The relations between chemical contents of the atmosphere, as well as the parameters of the process, structure and properties of the layer, have been defined. Iron phosphide reinforcement in the diffusive nitrided layer increases its hardness and resistance to wear.