The data obtained in experimental and few clinical studies indicate significant differences in the contents of the two main bacterial types (Firmicutes and Bacteroidetes) in type 2 diabetes mellitus (DM), although the results of different studies are often contradictory. In addition, there are no data in the literature on the changes in the content of the main types of intestinal microbiota depending on the severity of the course and compensation of diabetes. The aim – to study the content of the main phylotypes of the intestinal microbiota in patients with type 2 DM depending on diabetes severity and compensation. Material and methods. 64 patients with type 2 DM (29 men and 35 women) aged 30 to 72 years (mean age 47.3±8.9 years) and 30 healthy volunteers who made up the control group were examined. Clinical, laboratory and molecular genetic studies (DNA determination of Firmicutes, Bacteroidetes and Actinobacteria using quantitative real-time PCR and gene-targeted primers) were performed. Results. It was found that the content of Firmicutes in patients with type 2 DM was significantly higher, and the content of Bacteroidetes was significantly less than in healthy individuals. As the severity of DM increased and the compensation for type 2 DM impaired, the contents of Firmicutes also increased significantly, and the content of Bacteroidetes decreased, respectively, and the F / B ratio also increased. Conclusion. Certain disorders in the composition of the intestinal microbiota, in particular, decrease in the total number of Bacteroidetes, increase in the number of Firmicutes and F / B ratios, can play a pathogenetic role not only in the development of type 2 DM, but also contribute to its severity and compensation.