Objectives: It is well-known that saber sheath tracheal (SST) morphology is related to COPD and previous studies showed the positive correlation between tracheal index (TI) and forced expiratory volume at 1 second (FEV1). However, few studies evaluated the association between lung volume tests and TI measured by chest X-ray (CXR) or chest computed tomography (CT). Methods: A retrospective study was conducted with 43 COPD patients and 59 controls who had CT, CXR and lung function tests including spirometry and lung volume measurement. Tracheal parameter was used as TI, a ratio of tracheal transverse diameter to anteroposterior diameter. TI was measured at 1cm above the aortic arch. SST was defined as when the TI was less than 2/3. Results: In COPD group, TI value was significantly lower than one in the control group on CT scan, while TI measured on CXR were similar in two groups. Furthermore, SST defined from CT scan was significantly frequent in COPD patient (16.3% vs. 3.4%; p=0.023). However, TI was not related to any lung function parameters in COPD patients. Conclusion: Current study showed that SST was more frequent and TI was lower in COPD patient, while TI was not correlated with lung function including lung volume tests.