To improve the properties of nitrided surface, various post-treatment methods, one of which is post-aging, are applied on material surface. This study reports on tribological and corrosion properties of a post-aged AISI 4140 steel after plasma nitriding. In this sense, the post-aging treatments were performed for durations of 0.5, 1, 4, 8 and 12 h at a substrate temperature of 400 °C in plasma (50% H₂ and 50% Ar) and in furnace (100% Ar) atmospheres. After post-aging, the α″-Fe₁₆N₂ phase which has high hardness was formed by decomposing the compound layer. Due to increase in the diffusion rate of nitrogen in plasma atmosphere, the best hardness and wear properties were obtained in a short period of one hour. After an hour, overaging was observed. The corrosion resistance became worse in quenched and plasma post-aged specimens compared to nitrided AISI 4140. As a result, the maximum corrosion resistance was achieved in a furnace post-aging process due to the formation of an oxide layer on the surface.