Tetraalkylammonium molybdenum and rhenium thiometallates with different alkyl groups have been synthesized. The compounds obtained have been characterized by spectral and thermal methods. By thermosolvolysis of tetraalkylammonium thiometallates at 155-165 degrees C in a DMF medium, particles of MoS3 and Re2S7 sulfides soluble in nonpolar hydrocarbons owing to the treatment of their surface with surfactants (alkenylsuccinimide) have been prepared. The particle size of these sulfides ranges within 8-110 nm depending on the nature of the precursor. A high friction-reducing activity of molybdenum nanoparticles in a mineral lubricating oil medium and antiwear activity of rhenium nanoparticles in mineral and synthetic lubricating oils have been shown.