Plasma processing provides a useful tool for modifying the metallic and non-metallic surfaces. Plasma ion nitriding of M2 high-speed steel was carried out by using a low pressure plasma chamber and a 50 Hz pulsed DC source. By keeping the nitrogen-hydrogen (60:40) mixture pressure constant at 3 mbar and varying the plasma treatment time from 1 to 4 h, the nitriding was done in the abnormal glow region at 600°C substrate temperature. The resultant changes in surface properties of the plasma treated samples were investigated by using X-ray diffraction, scanning electron microscopy, and Vickers's microhardness testing. These investigations confirmed the formation of a compound layer on plasma exposed surface. The layer thickness was initially increased with nitriding time and then started to decrease after 2 h treatment. In X-ray diffraction data, a down-shift in the original diffraction peaks was noticed which confirms the nitrogen diffusion and formation of compound layer on the exposed surface. A significant improvement in surface hardness of tool steel was also seen especially after 2 h of plasma treatment. Copyright © Taylor & Francis Group, LLC.