Elemental analysis, molecular mass, and H-1 NMR data are presented for vacuum residue asphaltenes and the products of vacuum residue hydroconversion in the presence of nanosized MoS2 catalyst particles obtained "in situ" in the hydrocarbon medium. Structural group analysis of average asphaltene molecules has been performed and their structural units have been described. The main trends of change in the structural parameters of the molecules under the hydroconversion conditions and the effect of temperature on the character of these changes have been revealed.