A DeD 3/4 -containing composite nanocatalyst is synthesized in a hydrocarbon medium containing dissolved low-density polyethylene and is sulfided by dimethyl disulfide. The phase and structural compositions of the catalyst are determined. The activity of the composite nanocatalyst in the hydroconversion of West Siberian vacuum residue is investigated. It is shown that the catalyst performance depends on the way of its distribution in the feedstock. The efficiency of composite nanocatalyst DeD 3/4 -containing particles in hydroconversion is considerably improved when it is combined with the catalyst synthesized in situ.