Relevance. The need to modernize existing schemes and develop alternative methods of processing heavy hydrocarbon feedstock. To solve this problem it is necessary to study in detail the regularities of transformations of various components of such feedstock, in particular, sulfur-containing and resinous-asphaltene substances, in combined processes. Aim. To establish the impact of pre-oxidation on the regularities of changes to the structure-group characteristics of resin-asphaltene substances during vacuum gas oil cracking. Methods. Oxidation, liquid-adsorption chromatography, gas chromatography, X-ray fluorescence spectrometry, structural group analysis (the proton nuclear magnetic resonance (1H-NMR) spectroscopy, average molecular weight via cryoscopy in naphthalene, and elemental composition). Results. The paper describes the preliminary oxidation impact on thermal transformations and regularities of changes in the structural and group characteristics of resinous asphaltene substances of vacuum gas oil. It is shown that preliminary oxidative modification of vacuum gasoil with a mixture of hydrogen peroxide and formic acid allows significantly reducing the thermal stability of all its components, including resins and asphaltenes. The effect of such pretreatment on the structure of average molecules of these substances varies. It was established that oxidative modification leads to the appearance of thermally unstable fragments in the structure of resins, which are completely destroyed within an hour. An increase in the duration of cracking of both the initial and preliminary oxidation of vacuum gas oil leads to an increase in the proportion of two-block structures among the resin molecules (the blockiness of the molecules increases from 1.2 to 1.5) and the number of rings in them, primarily one – aromatic. Accordingly, the value of the aromaticity factor increases from 31.9 to 56.4–57.7. At the same time, the average molecules of asphaltenes of cracking products of oxidized vacuum gas oil represent larger structures than asphaltenes of cracking products of the initial sample, accumulating introduced oxygen in their composition. The block structure of the molecules is preserved (1.8–1.9), but the distribution of rings changes – the number of aromatic rings increases by one, and, accordingly, the aromaticity factor raises (from 61.3 to 64.9).