In spite of the huge worldwide interest for single-atom and ultradispersed catalysts, metal atoms coordinated with sulfur are rarely addressed. In this work, ultradispersed molybdenum-based catalysts were obtained by adsorption of three thiomolybdates of different nuclearity (n=1, 2, 3) on high-surface-area S-doped carbon, followed by sulfidation in H2S/H2 flow at 350 °C. Scanning transmission electron microscopy (STEM) and X-ray absorption spectroscopy (XAS) attest that single atoms and few-atom clusters are predominant on the surface of the materials after adsorption, as well as after sulfidation and thiophene HDS reaction. Independently on the nature of the thiomolybdate precursor, sulfidation leads to catalysts with specific thiophene HDS activity exceeding that of a conventional supported MoS2 reference. Ultradispersed clusters were further promoted with cobalt, yielding HDS turnover frequencies 2-3 times higher than those of reported benchmark CoMoS catalysts. These findings provide new insights into the previously debated issues of structure-activity relationships for HDS catalysts and expand the range of applications of atomically dispersed catalysts.