The tribological performance of lubricants containing TiO 2 nanoparticles and Molybdenum DiThioCarbamate (MoDTC) was investigated using a reciprocating ball-on-flat tribometer in steel–steel contacts. Lubricants containing only MoDTC were used for comparison. The influences of the additive concentration (0.1 wt% and 0.5 wt%) and of the roughness of the counterparts ( R a from 10 to 200 nm) on the performance of the lubricant were studied. Improved friction modification and anti-wear properties were found when TiO 2 nanoparticles were blended with MoDTC compared to MoDTC alone, even at low concentration and with rough surfaces. XPS characterizations and FIB-TEM analyses of tribofilms were performed and suggested that the formation of MoS 2 from MoDTC is favored in the presence of TiO 2 nanoparticles. The results are discussed, taking into account the tribocatalytic properties of TiO 2 nanoparticles.