Gastrointestinal endoscopy is one of the most frequent procedures, but relatively little is known about its pulmonary effects. Pulse oximeter is a convenient and non-invasive methods which monitors SaO2 and pluse rate. So, we studied the change of SaO2 and pluse rates during esophagogas-troduodenoscopy in the patients with impaired plumonary function and normal controls by pluse oximeter. In conclusion, the drop in SaO2 during endoscopy could occur in the pulmonary disease patients with mild to moderate imparied pulmonary function, but this change was transient and recovered rapidly during examination. So, we suppese that specific therapy such as O2 supply may not be requried durging endoscopy in these patients.