Endotracheal intubation is necessary in almost all cases of general anesthesia to maintain the airway. The endotracheal tube (ETT) sometimes causes airway obstruction secondary to secretions or other intraluminal materials, and it may cause hypoxemia and fatal outcomes [1,2]. We herein describe a case of a reversible ETT obstruction caused by meconium acting as a check valve, which was mistaken initially to be leakage from the anesthetic machine. The patient was a 1-day-old male infant (height, 43 cm; weight, 1.7 kg). He was born by cesarean delivery at gestational age 34 +3 weeks due to an omphalocele. The ruptured sac of the omphalocele (approximately 5 cm in diameter) was found at birth, and the emergency operation was planned. Before the surgery, he was already intubated because of meconium aspiration. In the operating room, initial blood pressure and heart rate were 52/32 mmHg and 160 /min, respectively, and SpO2 was 98%. A 3.0 mm uncuffed ETT had been placed at a depth of 8.5 cm, and a small amount of gas leakage was confirmed at the peak inflation pressure of 20 cmH 2O. Both lungs were clear by auscultation, and no secretions drained from the ETT upon suction. The patient underwent pressure-controlled ventilation using the following settings: inspiratory pressure, 15 cmH2O; respiratory rate, 30 /min; I : E ratio, 1 : 2. The tidal volume and end-tidal CO2 (ETCO2) were maintained at approximately 18–20 ml and 32–35 mmHg, respectively. SpO2 was maintained at > 95% during the operation. The surgeon repaired the entire intestine and began to close the abdominal cavity 3 hours after the surgical incision. Capnography showed an obstructive pattern, and ETCO2 increased slightly to 38–40 mmHg with no change in ventilator settings. We suctioned the ETT again using a 6-Fr suction tip, and there was no resistance or secretion. Upon completion of the abdominal closure, the surgeon decided to place an internal jugular venous catheter for postoperative care. The ventilator leakage alarm sounded during venous cut-down. The tidal volume decreased from 20 to 5–7 ml, and ETCO2 decreased to < 10 mmHg. The capnography curve exhibited a blunt concave slope during the expiratory phase. The ETT was confirmed to be positioned correctly, and there was little gas leakage around the ETT. A full examination of the anesthetic machine and breathing circuit, including capnography, revealed no abnormalities, but the SpO2 had decreased to 88%. Upon switching to manual ventilation during examination, we encountered resistance during the inspiratory phase. Chest auscultation revealed inspiratory rales and faint expiratory wheezing in both lung fields. The ETT suction was repeated, but no secretion was seen. The ETT was removed, and we reintubated with another 3.0 mm uncuffed ETT under direct laryngoscopy. The tidal volume was 20–25 ml at an inspiratory pressure of 15 cmH2O, and capnography showed a normal plot. The ETCO2 measured immediately after reintubation was 58 mmHg and decreased to 33–35 mmHg after hyperventilation for 3 minutes. Inspection of the removed ETT revealed thick meconium approximately 2 cm long plugging the distal lumen of the ETT. Additionally, an approximately 0.3 cm-long inspissated meconium was dangling from the superior portion of the inner wall