OBJECTIVE：To explore the effects of levothyroxine on the follicular helper T lymphocyte level of patients with Hashimoto’s thyroiditis. METHODS：51 patients with Hashimoto’s thyroiditis were selected as levothyroxine group， and another 30 healthy people were control group. Levothyroxine group was orally given 25-50 ug Levothyroxine sodium tablet， once a day， the dose was adjusted based on thyroid function， and the dose maintained when thyroid function turned normal， for continuous 90 d. Free triiodothyronine （FT3）， free thyroxine （FT4）， thyroid stimulating hormone （TSH） and the percentage of Th17 cells accounted for peripheral blood CD4+ T cells （Th17/CD4+） in levothyroxine group before and after treatment were observed and compared with control group， the correlation of Th17/CD4+ and thyroid function. RESULTS： After treatment， Th17/CD4+ level in levothyroxine group were significantly lower than before and higher than control group， the differences were statistically significant（P＜0.05）. TSH in levothyroxine group were significantly lower than before， FT3 and FT4 were significantly higher than before， the differences were statistically significant（P＜0.05）； compared with control group， the differences were not statistically significant（P＞0.05）. Th17/CD4+ showed positive correlation with thyroid function in levothyroxine group. CONCLUSIONS：Levothyroxine can significantly reduce the Th17/CD4+ and TSH， increase FT3 and FT4， and Th17/CD4+ is involved in the occurrence and progression of Hashimoto’s thyroiditis.