Oil-soluble Cu nanoparticles were prepared by an oil-water interface growth method, using ascorbic acid as a reductant, polyethylene glycol (PEG-2000) as a modifier, and 1-butanol as growth agent. The particle size distribution of the obtained nanoparticles was between 18.2-80.2 nm, and the average size was 44.7 nm. The microstructures of these nanoparticles were characterized by XRD, TEM and high-concentration laser granularity scatter analyzer. The XRD patterns indicate that the lattice parameters of these Cu nanoparticles are enlarged by about 1.478%. The anti-wear and friction performance of SF15W/40 lubricating oil with these Cu nanoparticles were measured by ball-on-disk UMT-Ⅱ tribometer. It is found that the oil-soluble Cu nanoparticles have wetting effect and can be kept in dispersing form for long-term in SF15W/40 lubricating oil; the tribological performance of SF15W/40 lubricating oil with nano-Cu is improved. The best additive content of oil-soluble nano-Cu in SF15W/40 is 0.8% (mass fraction), and in such case the friction coefficient and wear loss are the lowest