The XRD-based study investigates the macrostructural parameters of asphaltenes isolated from natural sulfur-rich asphaltite and from liquid conversion products of this asphaltite. The conversion was carried out in a supercritical water flow at 400°C and 30 MPa both in the absence and in the presence of aluminum and zinc additives. The XRD data demonstrate a decrease in the stack thickness (Lc) and in the number of aromatic sheets (M) in asphaltenes isolated from the conversion products compared to the initial asphaltite. On the other hand, the aromaticity (far) and the average aromatic sheet diameter (La) increase by a factor of nearly three; a significant rise is also observed in the proportion of stacked carbon atoms (φa). In the presence of metal additives, the differences are more pronounced. This is because the oxidation of zinc and aluminum in supercritical water, accompanied by heat release, increases the local temperature of the reactants and generates active hydrogen that prevents radical fragments from recombination.