Abstract： Objective:To investigate the clinical value of serum thyroid hormone level in diagnosis of lung cancer and monitoring of lymph node metastasis.Methods:A total of 79 patients with lung cancer from Department of Respiratory Medicine of the First Affiliated Hospital of Gannan Medical University or Department of Chest Oncology of Jiangxi Cancer Hospital were selectet as the lung cancer group, and 42 healthy subjects in the same period were selected as the health control group.Serum thyroid hormone levels, including free triiodothyronine (FT3), free thyroxine (FT4), total triiodothyronine (TT3), total thyroxine (TT4) and thyroid stimulating hormone (TSH) were measured by electrochemiluminescence assay in 79 patients with lung cancer and 42 healthy subjects.Serum FT3, FT4, TT3, TT4 and TSH levels in different groups of subjects were compared.Logistic regression analysis was used to identify the useful indicators, and receiver operating characteristic curve (ROC) analysis was used to evaluate the clinical value of various indicators in diagnosis of lung cancer and monitoring of lymph node metastasis.Results:Levels of serum FT3, FT4, TT3 and TT4 in lung cancer were significantly lower than those in healthy subjects ( P<0.001); the Logistic regression analysis showed that serum FT3 and FT4 were correlated with lung cancer diagnosis (all P<0.001); ROC analysis showed that the area under curve of serum FT3, FT4 and their joint detection in lung cancer diagnosis were 0.911, 0.887 and 0.945, respectively (all P<0.001). Levels of serum FT3 and TT3 were significantly lower in lung cancer with lymph node metastasis compared to those without lymph node metastasis (both P<0.001); the Logistic regression analysis showed that serum FT3 and TT3 were associated with lymph node metastasis in lung cancer (both P<0.05); ROC analysis showed that the area under curve of serum FT3, TT3 and their combined detection in lymph node metastasis monitoring were 0.796, 0.733 and 0.855, respectively (all P<0.001). Conclusions:Serum thyroid hormone levels have changed in lung cancer, and detection of serum thyroid hormone levels may offer valuable assistance for lung cancer diagnosis and lymph node metastasis monitoring.