Solvothermal one-step synthesis method was used for the preparation of ruthenium sulfide catalysts supported on the carbon black by the reaction of Ru-3(CO)(12) and sulfur powder with the carbon black in i-propanol. The carbon black acted as not only a supporting substrate but also a dispersing agent for ruthenium sulfide nanoparticles in the solvothermal one-step synthesis. The oxygen reduction properties of the products prepared by the solvothermal one-step synthesis were improved in comparison with those of the catalysts prepared by physically mixing the carbon black with the solvothermally prepared ruthenium sulfide powder.