Аннотация:The comprehensive study of mycobiota in full profiles of eutrophic peatlands based on abundanceand diversity rates has been carried out in order to broaden the knowledge on microorganisms’ biodiversity in wetland ecosystems and get a detailed understanding of their functioning. Thick eutrophic peatlands of forest and floodplain origin in Tver and Tomsk oblasts, Russia, were the objects of research. The abundance of fungi has been assessed by luminescent microscopic and plate methods. Culturable fungi were identified basing on their phenotypic features. All the numbers and rates acquired were analyzed considering that the peatland profile could be divided into acrotelm and catotelm layers. Samples were taken from the peatlands layer by layer with regard to botanical composition of peat in September 2019. The length of fungal mycelium varied in the studied peatlands from 195 m to 2.3 km per gram, the number of spores varied from 8 to 45 million spores per gram of dry peat. The fungal mycelium biomass differed (2–24 times) from peatland to peatland, whereas the fungal spore biomass was similar at all studied sites. Fungal biomass supplies in the studied peatlands, calculated for the whole profile, varied from 2 to 18.7 t/ha. Alder peatland (Alnus glutinosa) of forest origin was especially rich in fungal biomass. The proportion of fungal biomass in the acrotelm varied from 52 to 72% of total fungal biomass throughout all the peat profile. Culturable fungi were represented by 52 species of 32 genera. In the samples of analyzed fungi the representatives of genera: Mortierella, Cladosporium, Penicillium, and Trichoderma were the most widespread. The list of fungi species and the frequency of their occurrence are presented in the study. The Shannon’s biodiversity index varied from 1.8 to 2.5. The taxonomic similarity of the fungal complexes in the studied peatland in accordance with the Sørensen-Dice Index did not exceed 0.65.