The nitriding-quenching is a new surface modification method which consists of heating a steel at 973-1073K in a nitrogen/ammonia gas atmosphere followed by quenching. From the fundamental point of view, this unique technique was applied to low carbon steels to investigate basic features of this treatment. Microstructure observations, X-ray diffraction, electron probe microanalysis, X-ray residual stress measurement, tensile test, fatigue test, and corrosion test were performed. It is found that high nitrogen martensite was formed near the surface and the hardness was increased up to HV800, which was dependent on the volume of retained austenite and nitrogen concentration. The nitriding-quenched steel plates show high fatigue strength and lower corrosion current density in an active solution region.