The tribological property of nano-Cu as additive in lubricating oil was investigated on a stock-on-ring testing machine. Friction coefficient and wear mass loss were discussed in order to study tribological property. And the worn surfaces were characterized by scanning electronic microscopy(SEM). Then wear and lubricating mechanism were discussed. The results show that the wear and friction properties of nano-Cu as lubricating oil additive are excellent. And when the adding quantity is 0.04% and 0.03%(mass fraction), the friction coefficient and wear mass loss is best, respectively.