The patient was a 48-year-old woman, admitted for pleural effusion detected on chest X-ray in July 2005. Computer tomography(CT)scan showed massive pericardial and pleural effusion. We performed pericardial drainage, and the cytological diagnosis of the pericardial effusion was class V. Because endoscopic examination revealed advanced gastric cancer, we diagnosed it as gastric cancer complicated with carcinomatous pericarditis. The serum tissue polypeptide antigen(TPA) level was markedly elevated. In August 2005, we started combination chemotherapy using oral S-1(100mg/body/day; day 1- 21)and intravenous CDDP(100mg/body/day; day 8)for 5 weeks. After 2 courses, TPA was reduced and pericardial effusion disappeared. However, after 3 courses, pericardial effusion recurred. We changed treatment to weekly docetaxel. After 2 courses, we changed it to paclitaxel/CDDP. However, TPA was increased and pleural effusion and dyspnea occurred. There- fore, we changed to a course of combination chemotherapy using oral S-1(100mg/body/day; day 1-14)and intravenous CPT-11(100mg/body/day; day 1 and 8)for 4 weeks from March 2006. After 10 courses, we were unable to control pleural effusion, and dyspnea recurred. She died in December 2006. Gastric cancer complicated with carcinomatous pericarditis has a poor prognosis, but systemic chemotherapy mainly with S-1 was effective.