Plasma nitrocarburising and post oxidation were performed on SCM435 steel by a pulsed plasma ion nitriding system. Plasma oxidation resulted in the formation of a very thin ferritic oxide layer 1-2 μm thick on top of a 15~25 μm ε -F e 2?3 (N,C) nitrocarburized compound layer. The growth rate of oxide layer increased with the treatment temperature and time. However, the oxide layer was easily spalled from the compound layer either for both oxidation temperatures above 450 ? C , or for oxidation time more than 2 hrs at oxidation temperature 400 ? C . It was confirmed that the relative amount of Fe 2 O 3 , compared with e 3 O 4 , increased rapidly with the oxidation temperature. The amounts of γ '- Fe 4 (N,C) and θ - Fe 3 C, generated from dissociation from ε - Fe 2?3 /(N,C) phase during O 2 plasma sputtering, were also increased with the oxidation temperature.e.