Abstract: Based on experiments, the structure of Cu nanoparticles was characterized by transmission electronmicroscopy (TEM) and X-ray powder diffraction (XRD). The friction and wear tests of steel-steel tribo-pair lubrticated by oil with and without nano-Cu particles were counducted on a four ball tribo-tester for optimized concentration of nano-Cu particles. Comparisons on vibration,noise and temperature rise of motorized spindle were also included.. The results showed that the optimized concentration of Cu nanoparticle for the best tribological performance was 0.5%. Vibration, noise and temperature rise of motorized spindle with 0.5% Cu nanoparticle N32 as additive in oil were lower than that lubricated by pure N32 oil.