A pure iron (1 mm in thickness) was gas nitrided at 580 ℃ for 4h, followed by oil quenching or furnace cooling. The oil-quenched samples were first naturally aged (NA), and then artificially aged between 100 ℃and 140 ℃. The microstructural examinations and property characterization were investigated using X-ray di?ractometer, scanning electron microscope, transmission electron microscope, Vickers hardness tester and fatigue tester. It was found that the nitrided samples consisted of compound layers (CLs) and diffusion layers (DLs). The cooling method did not change the thickness of the CLs and the phase constitutes of the upper-most layer, but had remarkable effect on the microstructure and mechanical property of the DLs. A great quantity of rich-N clusters precipitated from the oil-quenched DLs after natural ageing for 200h, and the oil-quenched DLs had a great natural ageing strengthening phenomenon. During artificial ageing (AA), the type and number of precipitates could be controlled by the ageing temperature and ageing time. The main precipitates are the α″-Fe16N2 during lower temperature ageing while it is the γ′-Fe4N at higher temperature ageing. The NA samples could get very high hardness and strength. The hardness and strength of the AA samples decreased with the increase of ageing temperature. The high temperature ageing greatly improves the elongation of the oil-quenched samples. The CLs had little effect on the tensile stress of the nitrided samples, but greatly decreased the fatigue strength under the tensile.