The tribological behavior of graphite and Ag nanoparticles as solid additive to base oil was evaluated on a four-ball test machine and a disc-on-disc tribotester. Extreme pressure and anti-wear results are shown according to ASTM D4172 and D2783 standard methods. It is found that Ag nanoparticles have better anti-wear behavior, and especially the smaller size nanoparticle have better anti-wear behavior.