A gastro-pleuro-pericardial fistula is an abnormal communication between the stomach, pleural cavity, and pericardium. It is a very rare and life-threatening condition, which needs prompt intervention. We report a case of gastro-pleuro-pericardial fistula in a patient with tongue cancer who was treated with chemoradiotherapy. A 41-year-old woman presented with left chest discomfort and dyspnea. She was diagnosed with left pleural metastasis from tongue cancer and was treated with chemoradiotherapy on the left posteroinferior chest wall. A CT revealed the abnormal connection between the gastric fundus, left pleura and pericardium, showing gastro-pleuro-pericardial fistula.