A 3-month-old male infant underwent rigid bronchoscopy with manual jet ventilation due to persistent right upper lobe collapse under capnographic surveillance. The CO2 waveform abruptly vanished soon after application of jet ventilation, while breath sounds decreased gradually until the left side breath sounds were barely audible. Progressive abdominal distension with protruding umbilicus was also detected at the same time. Under the impression of bilateral tension pneumothorax, emergent needle decompression was carried out. In this case, the sudden onset of CO2 waveform change was the first warning sign of pneumothorax, which is the most common complication of jet ventilation. Therefore, we strongly recommend that continuous capnographic surveillance be applied during bronchoscopy with jet ventilation.