Background: Univent(R) tube was designed to overcome the disadvantages of double lumen endotracheal tube for one lung anesthesia. But overinflation of the blocker cuff of an endobronchial tube can cause pressure damage to the bronchus. The purpose of this study was to evaluate whether the blocker cuff pressure and the duration of ballooning using the Univent(R) tube is correlated with the degree of bronchial mucosal damage (BMD). Methods: A total of 13 men and 7 women intubated with the Univent(R) tube were enrolled for the study. The BMD were evaluated by direct visualization using fiberoptic bronchoscopy prior to intubation and following extubation and the degree of the BMD were scored from 0 to 4 as follows; 0: normal, 1: erythema, 2: swelling, 3: hemorrhage, 4: mucosal wall tearing. Results: No change in bronchial mucosa (score 0) were observed in 11 patients (55%), erythema (score 1) in 5 patients (25%), swelling (score 2) in 3 patients (15%), hemorrhage (score 3) in 1 patient (5%) and mucosal wall tearing (score 4) is none in 20 patients. The bronchial blocker cuff pressure required to "just sealing" the bronchus was 178.1+/-37.4 mmHg with corresponding cuff volume of 6.7+/-1.0 cc. The duration of ballooning was 115.5+/-26.4 min. The correlation coefficient between the blocker cuff pressure and duration of ballooning to the degree of bronchial mucosal damage were 0.125 and 0.137, respectively, which was not statistically significant. Conclusions: The bronchial blocker of Univent(R) tube doesn't cause any severe BMD and the degree of BMD are correlated with neither the bronchial blocker cuff pressure nor duration of ballooning of Univent(R) tube.