A case of cardiac tamponade because of metastasis from gastric cancer is reported. A 68-year-old man underwent distal gastrectomy for gastric cancer ten years earlier. Eight years after the surgery, he developed multiple bone metastases, which were recurrent gastric cancer, and he received systemic chemotherapy. He was admitted to our hospital with general malaise and anorexia. Computed tomography disclosed a large cardiac effusion. Cardiac tamponade and right-sided heart failure were diagnosed, and pericardiocentesis was performed. Cytodiagnosis of the pericardial effusion showed class V (poorly differentiated adenocarcinoma). His symptoms disappeared with drainage. After discharge from hospital, he refused chemotherapy. He died 12 months after the diagnosis of carcinomatous pericarditis, but no pericardial effusion re-appeared. It is rare that cardiac tamponade due to carcinomatous pericarditis develops from gastric cancer, but it requires emergency treatment. When a patient with recurrence of cancer presents with slight symptoms, the possibility of cardiac tamponade caused by carcinomatous pericarditis should be considered.