Abstract: Molybdenum disulfide (MoS2) nanopowder particles as a solid lubricant were prepared by chemical precipitation with ammonium molybdate and ammonium sulfide as raw material and grain alcohol as surfactant. The morphology and phase structure of MoS2 nanoparticles were characterized by transmission electron microscope (TEM) and X-ray diffraction (XRD), and its tribological properties were investigated on a vertical universal friction/wear tester. The worn surfaces of specimens were observed by scanning electron microscope (SEM) and the surface element composition was determined by means of energy dispersion spectrometry (EDS). The results showed that the MoS2 nanoparticles are spherical-shaped with mean particle size about 40-50 nm, and lots of dangling bond and their high surface energy/activity can play the role as solid lubricant in reducing greatly the friction coefficient of a friction pair so as to improve the wearability. It was found that the lubricating mechanism is that the powdered MoS2 nanoparticles are easy to be firmly adsorbed on rubbing surface to form a MoS2 thin film that will reacts chemically with metallic surface to become a wearable protecting film under high load at high temperature.