<p>The thiolation of iodobenzene and several (hetero)aryl halides using commercially available non-immobilized copper and copper oxide nanoparticles as catalysts was studied. Almost quantitative yields of diaryl sulfides were achieved using thiophenol and copper nanoparticles with an average size of 25 nm (5 mol.%) under optimized conditions (DMSO, 110 °C, Cs₂CO₃, the reagent concentration was 0.5 mol L⁻¹). Different-size and different-composition nanoparticles were compared with microsized Cu₂O and CuO or CuI powders in terms of efficiency; the nanoparticles showed a higher efficiency. It is demonstrated that copper nanoparticles can be recycled once in the reaction of iodobenzene with thiophenol without a yield decrease. The reaction was found to have an induction period and, according to the data on copper leaching during the reaction, the highest degree of leaching was at the initial stage and leaching strongly diminished by the end of the reaction. It is also shown that the solution still exhibits the catalytic activity after the reaction has been carried out. The obtained data suggest the main contribution of homogeneous catalysis. The transformation of nanoparticles in the course of the reaction was further studied by transmission electron microscopy.</p>