Background The airway obstructions are usually caused by secretions, mucus plugs, blood clots, malposition of bronchial blockers (BBs) cuff or twist of the tube by oral biting. In this paper, we report a case of accidental bronchial obstruction as a result of a cuff detaching from the BBs catheter.Case presentation A 48-year-old male was admitted to our department due to small cell lung cancer. He had received two cycles of neoadjuvant chemotherapy with etoposide plus cisplatin and was scheduled a right upper lobe resection by thoracotomy. During the surgery, the patient was intubated with an 8.0-mm internal diameter BBs tube (Univent tube). When the anesthesiologist tried to remove the BBs towards the end of surgery, the cuff got detached accidentally and obstructed the airway leading to improper expansion of the middle lobe. This condition was determined later by the 6.0-mm bronchoscope and the cuff was removed with forceps. Conclusions We report this case aiming to remind other colleagues that the cuff detachment in the surgical procedure is still a potentially fatal incident even it rarely happens nowadays. It is important to check the BBs apparatus meticulously through the whole operative procedure. The routine use of 4.0-mm bronchoscope should be highly recommended during the entire airway management when a bronchial obstruction is suspected.