The decrease of oil production with its simultaneous price increase and a growing demand for petroleum products leads to the importance increase of heavy hydrocarbon raw materials. The processing of heavy petroleum raw materials in water vapor using oxide type catalysts containing the metals of variable valence is a promising trend, but there are some problems for the study of liquid and solid conversion products of such raw materials that differ from traditional fractions of oil refining. There is the need to choose an informative research method that allows to analyze the structure and the composition of the products obtained quickly and with great accuracy. One of such methods is Fourier infrared spectroscopy method, widely used to study the structural-group composition of oil and petroleum products, which allows to determine more precisely the presence of certain functional groups in the composition of the products under study as compared to the chemical methods. Using Fourier infrared spectroscopy method, they studied the products of hydrothermal-catalytic conversion of heavy oil in a water vapor medium and in the presence of a natural hematite catalyst at the temperatures of 210, 250 and 300 °C. The effect of temperature and water content in the reaction mixture on the yield and the composition of experiment products is shown. Under the experimental conditions, a new formation of hydrocarbons takes place due to the destruction of high-molecular hydrocarbons, resins and asphaltenes. It has been established that the increase of temperature and the decrease of water content lead to the increase of test product aromaticity and oxidation degree with the development of insoluble asphaltene and coke product fraction. The method of Fourier infrared spectroscopy makes it possible to fix changes in the composition of products with a great accuracy and can serve as the control of heavy hydrocarbon raw material processing.