The tribological behaviors of various oxide nanoparticles, i.e. Bi₂O₃, CuO, SiO₂ and ZrO₂, added into a carbon fibers reinforced polyether-ether-ketone were comprehensively investigated. It was demonstrated that nanoparticle types played an important role in the tribological performance. When sliding took place at a low FV (load × speed) condition, the addition of CuO and ZrO₂ nanoparticles led to the formation of patch-like tribofilms increasing friction and wear. However, at FV factors ranging from 30 to 300 N m/s, the hard nanoparticles, i.e. SiO₂ and ZrO₂, resulted in dramatic improvement of the tribological properties. Moreover, nano-ZrO₂ was significantly more effective than nano-SiO₂ for enhancing the tribological performance. Hard nanoparticles released onto the sliding interface removed the tribo-oxidation layer on steel counterface. Hereafter, they were “tribo-sintered” into an oxide-based tribofilm having a high load-carrying capability. However, the soft nanoparticles, i.e. Bi₂O₃ and CuO, did not help to form a robust and lubricating tribofilm.