Abstract: Water-dispersible molybdenum disulfide (MoS2) nanoparticles were prepared via reduction of ammonium tetrathiomolybdate by ethylene glycol as the reducing agent anmd solvent as well. The microstructure of the product was characterized by means of X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. Moreover, the tribological behavior of the synthetic MoS2 as an additive in distilled water was evaluated by using a four-ball friction and wear tester, and the morphology and elemental composition of the wear scar of the steel balls were analyzed by means of scanning electron microscopy and energy dispersive spectrometry. Results indicated that the synthesized MoS2 nanoparticles were spherical-shaped and can effectively improve the friction-reducing and antiwear ability and increase the load-carrying of distilled water, showing promising potential in tribology as a kind of water-based lubricant additives.