Diamond-like carbons (DLC) with hardness of 47.1 GPa were coated on SUJ2 rollers, and their tribological properties were investigated after friction test under boundary lubrication conditions in an additive-free mineral-based oil at different testing oil temperatures of 24, 80 and 160 degrees C. From the results of the Raman analyses and Spectroscopy ellipsometry, we found that the structure changed of DLC at the topmost of sliding surface and their thickness will measured using AFM. It is found that the transformed layer increased with increases of testing oil temperature.