Objective To investigate the changes of thyroid hormone level in patients with nonsmall cell lung cancer ( NSCLC) before and after chemotherapy and its clinical significance.Methods 78 cases of NSCLC admitted between January 2009 and December 2011 were recruited in the study. The level of total triiodothyronine ( TT3 ) , total thyroxine ( TF4 ) , free triiodothyronine ( FT3 ) , free thyroxine ( FT4 ) , and thyroid stimulating hormone ( TSH) were measured by radioimmunoassay before and after chemotherapy. 35 normal subjects were recruited as control.Results The levels of TT3 [ ( 1. 27 ±0. 36) nmol /L vs. ( 2. 62 ±0. 46) nmol /L] and FT3 [ ( 2. 65 ±0. 76) pmol /L vs. ( 3. 79 ±0. 63) pmol /L] in the NSCLC patients were significantly lower than those in the controls ( P lt;0. 05) , while the levels of TT4 , FT4 and TSH were similar to the controls. The level of TT3 and FT3 were correlated with clinical stage ( P lt; 0. 05) , and not with histological grade and pathological type ( P gt;0. 05) . The levels of TT3 and FT3 were remarkably increased in complete remission or partial remission patients after chemotherapy ( P lt; 0. 05) . Conclusion Thyroid hormone measurement may be useful in the patients condition judgment and therapeutic effect monitoring.