Objectives: It is well known that the shape of flow-volume (F-V) curve is changed in patients with tracheal stenosis as well as unilateral main bronchial. However, there is no previous research for the evaluation of changes of F-V curve according to the degree of bronchial stenosis in these patients. Methods: We analyzed the expiration shape of F-V curve of 29 patients by graph digitizer program between 2005 and 2011 at the Samsung Medical Center. Results: The primary disease for unilateral main bronchial stenosis was endobronchial tuberculosis(86%), benign bronchial tumor(10%) and carcinoid(3%). All unilateral main bronchial stenosis were classified as 5 degrees (I: ＜25%, II: 26-50%, III: 51-75%, IV: 76-90%, V: 90-near complete obstruction without collapse of unilateral lung). There is only monophasic shape of F-V curve in degree I and biphasic in degree II to IV. In degree V, both monophasic shape(81%) and biphasic shape(18%) is observed. After standardized biphasic shape of F-V curve, the breaking point was compared. The breaking point of biphasic shape of F-V curve showed downward and rightward trend according to progression of stenosis (p＜0.001). Conclusions: The biphasic shape of expiration F-V curve in unilateral main bronchial stenosis is appeared according to progression of stenosis and disappeared with advanced stenosis. In addition, the shape of biphasic F-V is changed due to migration of breaking point according to progression of stenosis.