Objective:To observe the ratio of helper T cells 17 (Th17)/regulatory T cells (Treg) in peripheral blood of patients with Hashimoto's thyroiditis (HT) and the expression changes of related cytokines in serum, and to explore their role in the occurrence and development of HT.Methods:Using the case-control study method, 35 HT patients examined in the General Hospital of Heilongjiang Beidahuang Group from February to November 2019 were selected as HT group, and 39 healthy people in the same period were selected as control group. Early morning fasting venous blood samples of the two groups were collected to test the levels of thyroid stimulating hormone (TSH), free thyroxine (FT 4), thyroid peroxidase antibody (TPOAb) and thyroglobulin antibody (TgAb). The expressions of serum interleukin (IL)-6, IL-17 and transforming growth factor β (TGF-β) were tested by enzyme-linked immunosorbent assay (ELISA); the number of Th17, Treg in peripheral blood were determined by flow cytometry. Results:The levels of TPOAb, TgAb and TSH in HT group [130.60 (43.37, 714.40), 368.10 (136.90, 1 103.00) U/ml, 9.05 (6.62, 15.23) μU/ml] were significantly higher than those in control group [2.66 (1.52, 4.69), 12.63 (11.43, 14.60) U/ml, 1.87 (1.36, 2.23) μU/ml, U = 6.87, 6.62, 4.85, P < 0.001], and the FT 4 level [0.76 (0.63, 1.04) ng/dl] was lower than that in control group [1.14 (1.02, 1.26) ng/dl, U = 7.39, P < 0.001]. The expressions of IL-6, IL-17 and TGF-β in HT group were higher than those in control group ( t = 2.41, 9.04, 2.44, P < 0.05). The number of Th17 and the ratio of Th17/Treg in HT group were higher than those in control group ( t = 4.20, 3.50, P < 0.05), and the number of Treg was lower than that in control group ( t = 4.45, P = 0.001). Conclusion:In HT patients, Th17 are increased, Treg decreased, Th17/Treg ratio increased, and the expressions of IL-6, IL-17 and TGF-β are increased.