As air travel has become part of the fabric of modern life, travel opportunities have increased for individuals who have serious medical conditions, including underlying lung disease & COPD patients. Apparently, it is incumbent upon physicians to understand the physiologically hostile environment that air travel posses to patients with limited cardiopulmonary reserve, in particularly COPD. In our study we try to evaluate the effect of hypobaric hypoxia on patients with COPD by comparing the siprometric measurements changes and arterial blood gases changes between these patients and normal healthy individuals at sea level and during moderate acute hypobaric hypoxia as occurs during air travel. Forty COPD patients and normal healthy adults were enrolled in this study. Siprometric measurements & arterial blood gases was done to both groups at sea level and repeated at 8000 ft. in a man-rated hypobaric chamber. The results obtained from both groups were collected, tabulated, statistically analyzed and compared. The overall results obtained showed significant reduction of PaO2, PaCO2, oxygen saturation and FVC & rise in the PH in both groups on exposure to 8000 feet. When the results of each group were compared with one another, it showed significant increase in the magnitude of decline of PaO2 and oxygen saturation in COPD patients as compared with normal healthy individuals. In a trial to estimate the altitude PaO2 in COPD patients, we could formulate a regression equation with definable accuracy using PaO2 at sea level as follows:Y= A+BX whereY= PaO2 at 8000 ft. and X=PaO2 at sea levelA=-14.5 and B=0.94 This study also showed that COPD patients with sea level PaO2 less the 74.4 (+/- 2.4)mmHg is most likely to have an altitude PaO2 les than 50 mmHg, and that these patients should be considered as high risk group and are most likely to need in-flight oxygen administration. In conclusion COPD patients are at risk of hypoxia if exposed to altitude or during using commercial aircraft if compared with normal healthy adults. Careful preflight evaluation of this group is needed in order to avoid serious complications that may affect those patients during or even after using commercial aircrafts. Sea level PaO2 and regression equations using sea level PaO2 may be used to screen COPD patients who are at increased risk of in-flight problems and who are in need for in-flight oxygen therapy.