Several cases of pulmonary air embolisms during surgery have been reported. However, such incidences are very rare during endoscopic surgeries. A 5-year-old boy with third ventricular arachnoid cyst and hydrocephalus underwent endoscopic third ventriculostomy under the general anesthesia, during which continuous intraventricular irrigation was maintained with normal saline. During the procedure, arterial and transcutaneous oxygen tension and end-tidal carbon dioxide tension became suddenly decreased while arterial carbon dioxide tension increased. Within 3 minutes after the inspired gas mixture was changed to 100% oxygen, the patient's respiratory variables returned to near base line. The second attack occured about 10 minutes later and decreased arterial oxygen tension with increased arterial carbon dioxide tension continued for about 5 minutes. After waking up from anesthesia, the patient suffered a generalized seizure attacks that was managed with anticonvusant therapy. We believe that we are the first to report an attack of pulmonary air emblism during brain endoscopic procedure. It was reported with the review of literatures.