In this study, the tribological behaviors of fullerene nanoparticles-added mineral oil were investigated as a function of viscosities (e.g., 12, 30, 55, 96 and $145;mm^2/s$). Extreme pressure and anti-wear properties were evaluated using a four-ball tester, respectively. The lubrication tests were performed with a disk-on-disk tester for different normal loads. Tribological properties were evaluated by measuring friction surface temperature and the friction coefficient, and interpreted in terms of the Stribeck curve. We note that the weld points of the raw- and nano-oil increased as the oil viscosity increased and weld points for all nano-oil were higher than those of raw oil. Also the wear scar diameters of the raw- and nano-oil decreased as the oil viscosity increased and wear scar diameters for all nano-oil were less than those of raw oil. Also, we have found that the difference of friction coefficient between raw oil and nano-oil was outstanding when the viscosity of raw oil was low and the normal load is high. Our results indicate that the addition of fullerene additives in lubricant was more effective when the viscosity of raw oil was low under the higher normal load conditions.