Abstract: The tribological properties of single and mixed nano-particles of WS2 and MoS2 as lubricant additives were investigated by using a four-ball tester. The surface morphology of wear scar was observed by inverted metallurgic microscope, the chemical states of several typical elements on the worn surfaces were examined by scanning energy dispersive X-ray spectrometer, and the lube oil samples after abrasion test were analyzed by ferrograph. Test results show that these two nano-particles additives both exhibit excellent tribological properties due to forming adsorption-chemical reaction mixed protection films on the surfaces of the friction pair during lubrication action, as a result, the main wear mechanisms of the surface might change, so that the lube oil displays good anti-wear, friction-reducing and extreme pressure properties. Furthermore, the mixed nano-particles show better anti-wear and friction-reducing properties than those of the single ones, though its extreme pressure property was rather weak.