This work reports the reduction of sulfoxides with boranes, in excellent yields, catalyzed by oxo-rhenium complexes (1 mol %) at room temperature under air atmosphere. The best results were obtained with catecholboranc (H Bcat) in the catalytic systems H Bcat/ReIO2(PPh3)(2), H Bcat/Re2O7, and H Bcat/MTO. DFT calculations were performed for the system based on ReIO2(PPh3)(2), which was studied in more detail. The reaction starts with the formation of ReIO2(R2SO)(2), followed by addition of the first molecule of H Bcat and loss of R2S. In a second step, a second H Bcat molecule attacks the Re(VII) intermediate, reducing the metal back to Re(V), while H-2 and cat BOBcat are released and the Re catalyst is regenerated, reentering the reaction cycle. The computed reaction barriers are much lower than those for any alternative pathway that could be envisaged.