We describe our experience with a 60-year-old man who had severe airway obstruction during one-lung ventilation with the tracheostomy tube using a bronchial blocker. The blocker, deriving from Univent tube, was passed through the tracheostomy tube and placed in the right main bronchus. We checked that the blocker was in appropriate place with a bronchofiberscope and obtained good one-lung ventilation with the patient in the left lateral position. However, just after the start of operation, when the skin was incised, sever hypoxia and resultant bradycardia and hypotension occurred, probably because of not only malposition of blocker but also atelectasis in the upper lobe of the dependent lung by secretion.