In this work, the effect of modulation period (A) on Ti/TiN multilayer films deposited on high-speed-steel (HSS) substrates using pulse biased arc ion plating is reported. The crystallography structures and crosssectional morphology of Ti/TiN multilayer films were characterized by X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM), respectively. Their mechanical properties were determined via nanoindentation measurements, while the film/substrate adhesion via the scratch test. It was found that the highest hardness value reached 43 GPa for the modulation period of 54 nm, while the film/substrate adhesion also reached the highest value of 83 N. Furthermore, the hardness enhancement mechanism in the multilayer films is discussed. (C) 2010 Elsevier B.V. All rights reserved.