Abstract: In-situ synthesis process was used to prepare copper nanoparticles and coppernanoparticles-polyethylene glycol oil solution by reduction of copper acetate by glycol in polyethylene glycol containing amido ligand as dispersant. XRD and TEM analysis proved that as-prepared samples containing copper nanoparticles with grain-size of about 5 nm. Tribological behaviors of nano-Cu in PEG-400 were investigated on a four ball machine. Result shows that addition of nano-Cu can greatly improve anti-wear and friction reduction properties of PEG-400. X-ray photoelectron spectroscopy (XPS) and energy dispersive spectrometry (EDS) analysis reveal that tribo-film composed of copper and minor cuprous oxide was formed on the worn surface, which might attributed to the excellent tribological properties.