PURPOSE: The relationship between non-alcoholic fatty liver disease (NAFLD) and thyroid function is controversial. A mild acquired thyroid hormone resistance may exist and explain these contradictions. This study aims to investigate the associations of thyroid hormone sensitivity with NAFLD and the severity of liver fibrosis in euthyroid populations. PATIENTS AND METHODS: Twenty-nine thousand three hundred and eighty-six adult subjects were recruited from the medical examination center of the Beijing Chao-Yang Hospital. Free triiodothyronine (FT3)/free thyroxine (FT4), thyroid feedback quartile-based index for FT4 (TFQI RESULTS: Euthyroid adults with NAFLD had elevated levels of serum FT3 and FT4, reduced TSH, and impaired sensitivity to thyroid hormones. Compared with participants in the first quartile group, the risk of NAFLD was higher in the fourth quartile of TFQI CONCLUSION: Impaired central sensitivity to FT3 and higher FT3/FT4 were associated with increased risks of NAFLD and related metabolic disorders. In patients with NAFLD, higher FT3/FT4 correlated with its progression to liver fibrosis. These findings might provide novel insight into the monitoring and evaluation of the risk of NAFLD and the severity of liver fibrosis.