Medium carbon steel (EN8) substrates with different Surface Roughness (SR) were deposited by Titanium Nitride (TiN). The research work was carried out to investigate the effect of SR and thickness of the thin film coating on substrate structure and tribological properties. EN8 rectangular blocks (60x10x10mm) were used as substrate materials. The variations in SR were achieved by using emery paper on one side and by machining the other side. Scratch tests were conducted and they showed that TiN coatings on substrate with higher SR (1.2 µm) exhibited less adhesion strength compared to TiN coatings on substrate with a lower SR (0.4 µm). Scratch tests also indicated poor adhesion with an increase in the SR of the substrate. The traction force and Coefficient of Friction (COF) were measured during the dry scratch tests under different normal loads, sliding speeds and ramp load conditions. To examine the morphologies of coated substrates and worn surfaces after the scratch test, optical microscopy was utilized. It was found out that TiN coating with a substrate roughness of 0.4 µm exhibited a lower COF and its wear mechanism was adhesive wear. It was experimentally found out that by decreasing the SR of the substrate coatings, wear resistance could be improved.