In the present work, surface-coated Cu nanoparticles with FCC structure and an average size of 40 nm were prepared by reducing reaction and surface modification technique. The morphology and phase structure of the nano-copper were characterized by transmission electron microscope (TEM). The ball-on-disc tester and ring-on-block tester were performed to study the tribological properties of surface-coated Cu nanoparticles as oil additive. The tests were carried out under the lubrication of 50CC oil alone and oil containing surface-coated nano-copper additives. The morphologies and elementary distributions of the worn surfaces were analyzed by scanning electron microscope (SEM) and energy dispersive spectrometry (EDS), respectively. Results indicate that surface-coated nano-copper additives can significantly improve the wear resistance and load-carrying abilities of 50CC oil, as well as reduce friction coefficient. A soft copper protective film is formed on the worn surface lubricated with oil containing nano-copper additives, which separates the worn surfaces, avoids their direct contact and reduces friction and adhesive wear. Besides, the grooves and small valleys on the worn surfaces are found to be partly filled and repaired by nano-copper, as makes the worn surface repaired and smoother.