This study was performed with the aim of evaluating the relative frictional behavior of (Ti 1-x Al x ) N coatings commercially deposited on H13 hot work tool steel. By using an arc ion plating PVD technique, TiN and TiAlN coatings with thickness of 3-5 µm were produced on steel specimens. The coatings were characterized using X-ray diffraction, optical microscope, scanning electron microscopy, energy-dispersive X-ray analysis, nano-indentation, atomic force microscopy and wear testing. Tribological behavior of the PVD-titanium aluminum nitride (TiAlN) coated in dry sliding against 52100 steel counterparts was investigated using the pin-on-disk standard test with varying sliding speeds and normal loads. For this study, the dry sliding wear experiments were conducted at two contact loads, 1 N and 3 N, and three sliding speeds, 0.1, 0.2 and 0.4 m/s. The wear mechanisms are discussed together with the morphological characteristic, determined by SEM analysis. Abrasive and adhesive wear were identified as the main mechanisms of wear in both TiAlN and TiN coatings followed by generation of oxides. It was observed that the friction coefficient of TiAlN coating was lower than that of TiN. The Results suggested that TiAlN coatings may be more advantageous than TiN coatings for high speed application where higher temperatures are involved. Furthermore, the effects of sliding speed, moisture, applied load, and surface roughness on friction coefficient of the coatings were investigated. In the second part of this research, effect of Aluminum content on mechanical and tribological properties of TiAlN coatings, hardness, morphology, roughness, structure and friction coefficient, were studied. In the third section, the friction coefficient of TiN and TiAlN coatings improved by oxidation were investigated. Oxidation took place in an electrical furnace with air atmosphere at 400, 500, 600, 700 and 800 degrees centigrade. Diffusion depth and oxygen content were estimated by EDS analysis. The effect of aluminum concentration (0 and 60 at. %) on the low-temperature oxidation behavior of TiAlN films was explored. The structure of oxide layers formed during oxidation was characterized using an X-ray diffractometer (XRD). Surface morphology and cross-sectional evaluations of the oxides were carried out by scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS). An aluminum-rich oxide layer was formed on the surface of coatings due to the outward diffusion of aluminum during oxidation. The composition and distribution of the oxidizing layers over TiAlN films were investigated. The results indicated that oxidation resistance increased as the aluminum concentration was increased. The type and location of oxidizing phases were dependent on the aluminum concentration. Two major oxides, Al 2 O 3 and TiO 2 were observed. Protective layer formed on the surface was TiAlON and this oxide layer played a role as the barrier against further oxygen diffusion. As a result of oxygen diffusion in TiN lattice, TiAlON phase was formed which act like a solid lubricant and decreased the friction coefficient of TiAlN coatings. Based on the experimental results, appropriate chemical composition and heat treatment cycle for optimum frictional properties of TiAlN coatings were presented. Key words: TiAlN, Friction, PVD, Aluminum, oxide, Surface oxidation.