Th17 and Treg cells play an important role in maintaining immune homeostasis. Disruption of the balance of these cells can lead to inflammatory bowel diseases, including ulcerative colitis. The level of FOXP3 (a characteristic marker for Treg cells) and RORC (a characteristic marker for Th17) gene transcripts in peripheral blood leukocytes of healthy people and patients with ulcerative colitis was studied. The mRNA content of FOXP3 and RORC genes in the peripheral blood of patients with ulcerative colitis was shown to be higher than in people from the control group (p = 0.0093, p = 0.0008, respectively). The ratio of the FOXP3 and RORCgene mRNA levels in peripheral blood leukocytes of healthy people was 2.57, in patients with ulcerative colitis - 1.91. To assess the relative content of Treg cells with the CD4+CD25+CD127lo/-phenotype and Th17 cells with the CD4+CD161+ phenotype in the peripheral blood, cytometric analysis was used. No significant differences in the number of these cells in healthy individuals and patients with ulcerative colitis (p = 0.14, p = 0.11, respectively) were found. In our opinion, an increase in the expression level of the FOXP3 and RORC genes in the peripheral blood leukocytes of patients with ulcerative colitis indicates activation of the T-cell link of adaptive immunity. The presence of differences in the transcriptional activity of the genes characterizing Treg and Th17 cells and their absence in the number of CD4+CD25+CD127lo/- and CD4+CD161+ cells in individuals from the study groups is probably associated with the diversity of subpopulations of effector and regulatory T lymphocytes expressing the indicated transcription factors.