In order to clarify the effect of deformation prior to nitriding and additive elements on nitriding behavior in pure iron and Fe-M（M＝Al, Cr）binary ferritic alloys, which had been deformed by HPT processes, were plasma-nitrided at 843K for 3.6ks, then the microstructure and hardness of them were investigated. It was found that the effects of deformation on hardness of nitriding diffusion zone in pure iron and Fe-1Cr alloy were small. In contrast, the hardness of diffusion zone in Fe-1Al alloy was greatly increased by deformation because deformation promoted the precipitation of AlN more extensively than non-deformed specimen. In addition, deformation resulted in more homogeneous growth of the compound layer with the finer grain size of γ’ on the compound layer. This feature was observed most remarkably in Fe-1Al alloy, where needle-like γ’ compound layer was formed in the non-deformed specimens.