Pulmonary aspiration is one of the most common complications and leading cause of high morbidity and mortality from tracheal intubation under mechanical ventilation. We experienced a case of severe aspiration pneumonia leading to death in a sixty-year old male patient who was under mechanical ventilation due to sepsis after intestinal perforation. In his past history, he had undergone a radical total gastrectomy due to advanced gastric cancer, and this time, he got almost a total small bowel resection due to small bowel perforation and gangrenous change. He was admitted to the Surgical ICU for postoperative care due to sepsis. At first his condition was very poor. Aggressive therapy with hemodynamic monitoring was performed, and there had been much improvement in his condition. On the 8 th ICU day, there was a large amount out of greenish intestinal fluid and increased endotracheal secretions of the same color. At that time, there was no air leak around the trachea and his tidal volume on ventilator was the same as before. The pH of aspirated fluid was 6.8 and E. coli was cultured. Two days later, there was a diffuse ground glass appearance on the entire right lung field on his chest X-ray. On the 11 th ICU day, he expired.