We report a case of a 23-year-old womanwho developed pulmonary embolism(PE)during chemotherapy for advanced gastric cancer following total gastrectomy(R1). She presented with type 4 gastric cancer with peritoneal dissemination and positive washing cytology. Palliative total gastrectomy was performed(R1)and first-line chemotherapy with S-1(80mg/m2, days 1 to 21) plus CDDP(60mg/m2, day 8)(SP; every 35 days)was administered. PE occurred on day 15 of the 3rd courses of SP. Computed tomography(CT)revealed massive PE in both the pulmonary arteries, and ultrasonography indicated an increase in right-sided pressure. Thrombolysis using urokinase and heparin was performed immediately, and she recovered after 10 days in intensive care. Dehydration caused by the adverse event, as well as nausea and the anticancer drug itself, are risk factors for DVT and PE. Risk stratification, prevention, and early treatment are very important for PE.