Chronic obstructive pulmonary disease (COPD), a group of diseases of distinct aetio-pathological consideration with different phenotypic presentations where smoking is the leading cause, all share the ultimate result of airflow limitation. This study aimed to evaluate thyroid function tests (TFT) in patients with COPD. Pulmonary function tests (PFT) were performed for 30 patients with obstructive lung disease and fifteen healthy control individuals. We measured SPO₂ to confirm COPD and assess the severity of the disease and assessed TT3, TT4, and TSH using the ELISA test. The values of VC, FVC, and FEV in the first second and PEF, TSH, and SPO₂ were lower in the COPD group than in the control group (P-value=0.001). In severe COPD (FEV₁<50%), there was a significant reduction in T3 but not T4 or TSH compared to mild-moderate COPD patients. Thyroid dysfunction was observed in patients with COPD pointing to a metabolic response; patients with lower weight indices had a lower TSH and, consequently, T3.