The purpose of this study is to investigate the effects of pulse ratio on the surface characteristics of the plasma nitrided and DLC coated high speed steels. In duplex treatments, micro-pulsed plasma nitriding was performed with N₂ and H₂ gases at 530℃, for 4hours. Pulse ratios were controlled within ranges from 0.1 to 1 by varing both the pulse on time and the pulse off time. Plasma assisted chemical vapor deposition(PACVD) equipment was used for the deposition of diamond-like carbon films. Since the film to substrate adhesion is of primary importance for the industrial application of the duplex layers, critical load was measured by the scratch test method. Properties of the nitrided and duplex treated layer were analysed by using optical microscopy, scanning electron microscopy(SEM), X-ray diffractometer(XRD), atomic force microscopy(AFM) and micro-vickers hardness tester. It was found that surface roughness was increased with increasing of pulse ratio for all the nitrided and duplex treated surfaces. The critical load to failure was decreased with increasing of substrate roughness.