Surface-modified nanoparticles of molybdenum trisulfide were obtained by the hydrogen sulfide treatment of inverse microemulsions of molybdic acid salts. The structure of the nanoparticles was studied by IR and NMR spectroscopy. The molybdenum nanoparticles were proposed for use as antioxidant and friction reducing additives to lubricating oils. It was shown that an anion-exchange reaction occurred between cetyltrimethylammonium bromide used to stabilize a inverse microemulsion and thiomolybdate, which had been formed in the system as a result of the replacement of oxygen atoms in the starting molybdate with sulfur by the action of hydrogen sulfide. Isolated molybdenum trisulfide nanoparticles in organic solvents, including hydrocarbons, can be dissolved by treating the nanoparticle surface with nitrogen-containing modifiers, which are attached to the sulfur-containing core of nanoparticles, probably via a Mo-N bond. A plausible model for the structure of modified MoS3 nanoparticles is proposed.