Due to various factors, the number of chronic obstructive pulmonary disease (COPD) patients continues to increase. In addition, the mortality from COPD is increasing because of the difficult in the early detection of COPD. Radiologic and respiratory examinations should be performed simultaneously for improving the diagnostic accuracy of COPD. But a conventional respiratory examination leads to diagnostic inaccuracy and decreases the reproducibility of examinations because there is air leakage between spirometry and mouth. Also, it is difficult to apply for all ages. In this study, we confirmed the possibility of material decomposition for pulmonary function test by combining dual-energy X-ray images obtained from a photon counting detector. Non-radioactive Xe, which appears in X-ray images, was also used. The RMSE of each material in decomposed images was analyzed to quantitatively evaluate of the possibility of material decomposition for pulmonary function test. Results showed that the average RMSE values of PMMA, lung and nonradioactive Xe were 0.005, 0.0199 and 0.0217, respectively, and we observed the high accuracy of material decomposition. Therefore, the diagnosis of COPD can be simplified through the material decomposition imaging using non-radiologic Xe, and the lung function can be evaluated by decomposing the total lung and actual gas exchange areas.