Silver/polydopamine (Ag/PDA) nanocomposite powders were synthesized by dropping the AgNO₃ solution into aqueous solution containing dopamine (DA) molecules. The friction and wear properties of oil-acid (OA) modified Ag/PDA composites as additives in poly-alpha-olefin (PAO) base oil were measured using four-ball tribometer under different loads. The results show that the PAO containing OA modified Ag/PDA nanoparticles (OAMAgPDA) exhibit a better tribological property than pure PAO. The maximum decrease in wear scar diameter (WSD) and friction coefficient are amounted to 40% and 30%, respectively. The tribofilm containing C, O, N, Ag and Fe exists and plays an important role on reducing friction and increasing wear resistance.