Nanosized and ultrafine dispersions of sulfided molybdenum catalysts are synthesized from reverse emulsions in the medium of vacuum residue using various molybdenum-containing components and sulfiding agents and temperatures and times of synthesis. Physicochemical methods are applied to investigate the size, dispersion state, composition, and structure of the dispersed phase and their dependence on synthesis conditions. The hydroconversion of West Siberian vacuum residue in the presence of a number of ex situ synthesized sulfided molybdenum-containing catalyst particles is conducted. It is found that they show high activity in suppression of the polycondensation reaction leading to coke formation.