Grease plays important roles in reducing frictional loss and providing protection of rubbing surfaces. In this research, we investigated the effects of -zirconium phosphate nanoparticles as additives in grease on the galling behavior of a pair of steels (4130 against P530). The results showed that the addition of 0.5wt% of nanoparticles in petroleum jelly could reduce the friction for 10% and the area being galled for 80%. In terms of particle sizes, the 1m sized particles have profound influence in galling reduction. This is due to the increased contribution of van der Waals forces in the stacked layers of those particles. Under shear, those particles are exfoliated, resulting in low friction and more surface coverage to protect surfaces from galling.