How to make full use of the synergistic effect between nanomaterials is of great significance for designing high-performance lubricating materials. Here, novel amine-terminated ionic liquid-modified graphene oxide (GO)/copper nanocomposite (IL-GO/Cu) is synthesized by facile liquid-phase method in which GO nanosheets and Cu nanoparticles are linked by 1-aminoethyl-3-methyl imidazolium nitrate ionic liquid through covalently grafting and electrostatic interaction. Of what interest is the homogeneous distribution of Cu nanoparticles on IL-GO plane/interlayers, possibly being endowed to excellent lubrication function. Results demonstrate that IL-GO/Cu nanocomposite with 0.08 wt% addition amount into polyethylene glycol (PEG 200) improves friction and wear resistance by up to 40.1% and 47%, respectively. Such performance characteristics mainly depend on the synergistic lubrication, including not only the boundary lubrication film composed of adsorbed/transfer/tribochemical film, but also the "third body" from the additive and its wear debris with Fe/Cu nanocrystals-embedded graphene-like structure. This paper offers an attractive strategy for fabricating graphene-based nanocomposite toward real-world application in tribology.