Diameter of nanoparticles plays a vital role in tribological properties of lubricanting oil. Three kinds of nano-copper with different diameters (50nm, 65nm, 80nm) were produced using the electric explosion of metallic wire (EEW), and their diameters were characterized by Scanning Electron Microscope (SEM). The tribological properties of the lubricating oils containing nano-copper additives were investigated using friction wear testing machine, and the wear scar morphology photographs were observed by means of continuously multiple microscope. The results show that lubricanting oil with the large diameter of 80nm copper particles and the weight percentage of 1.0% ~ 1.2% has good characteristic of extreme pressure ; while the lubricanting oil with the small diameter of 50nm copper particles and the weight percentage of 1.2% provides good properties of anti-wear and friction reducing. This has a guiding role in selecting nanooil additives.