Abstract <p>The article presents the results of a study of unoxidized and naturally oxidized (weathered) brown and hard coals of early diagenesis and humic acids (HAs) and fulvic acids (FAs) obtained from them. Using ¹³C NMR (CP/MAS) spectroscopy, it was found that the structural-group composition of the isolated HAs was determined by the composition of the original coals (<i>R</i>² = 0.81), and it affected the magnitude of biological activity using wheat seeds as an example (<i>R</i>² = 0.75). The structural-group composition of the isolated FAs was weakly related to the composition of the original coals, and it was more homogeneous. The high quantitative yield and biological activity of HAs and FAs from unoxidized and oxidized brown coals allowed us to recommend them for agriculture. The HAs and FAs from oxidized coals had low biological activity, and they can be considered as technical reagents.</p>