Abstract: Nitrided layer was prepared on 38CrMoAl steel surface by using ammonia gas as the nitriding medium in a gas nitriding oven. The effect of rare earth La doping on the microstructure, toughness and erosion resistance of the nitrided layers was ionvestigated by means of optical microscopy, scanning electron microscopy, transmission electron microscopy, and erosion wear testing. The results show that rare earth element La helps to improve the microstructure of nitrided layers by way of micro alloying effect which is dependent on its permeation into the nitrided layers. Subsequently the toughness and erosion resistance of La nitrided layer are increased significantly as compared with the conventional nitrided layer. The erosion wear of conventional nitrided layer is characteristic of plate like peeling and plastic deformation, accompanied with cross cracks and peeling of larger wear debris, that of nitrided layer containing La is dominant by plate like peeling and plastic deformation.