This work reports tribological properties of PAO6 containing SiO2 nanoparticles modified with stearic-acid (SiO2-SA) as additives at concentrations (0.05, 0.10, 0.20, 0.30 wt%) and the same concentration of SA as a dispersant. Tribological experiments were performed at 120 °C in pure sliding and rolling-sliding conditions (5% slide-to-roll ratio). All nanolubricants have better anti-friction capabilities than PAO6. The optimum concentration for friction reduction was 0.30 wt% for both tribological conditions. The best anti-wear results for the specimens tested in pure sliding conditions were achieved with PAO6 + 0.20 wt% SiO2-SA with reductions of 55%, 86% and 92%, in wear track width, wear track depth and wear area, respectively. Tribological mechanisms of the nanoparticles have been analyzed through roughness measurements, concluding that polishing, tribofilm and adsorption of the additives occur.