Abstract <p>The article presents the results of a study of the structure of humic acids isolated from brown coals of Yakutia and oxidized coals of Kuzbass using nuclear magnetic resonance spectroscopy and IR spectroscopy. Based on the ¹³C NMR spectra, their structural parameters, such as the aromaticity index and hydrophobicity index, were calculated. It was noted that the humic acids of oxidized coals were characterized by higher values of the aromaticity and hydrophobicity indices than those of the humic acids of brown coals. The&#xa0;results of titrimetric analysis showed that humic acids isolated from oxidized coals were characterized by a higher concentration of carboxyl and carbonyl groups. Based on the study, it was suggested that the humic acids of brown coals from Yakutia will have stronger growth-stimulating properties than the humic acids of oxidized coals from Kuzbass.</p>