A 51-year-old woman with edema of the lower extremities and exertional dyspnea was admitted to our hospital. Enhanced CT revealed thrombi of the pulmonary artery and a gallbladder tumor. After anticoagulation therapy was started on her, anemia and jaundice progressed; thus, endoscopic retrograde cholangiopancreatography(ERCP)was performed on suspicion of bleeding from a gallbladder tumor. We performed cholecystectomy in emergency to control the anemia due to hemorrhage. Oxygenation suddenly worsened intraoperatively, maintaining her blood pressure became difficult, and the patient decompensated. The histopathological diagnosis was gallbladder mucinous carcinoma with severe lymphatic invasion. Although an autopsy was not performed, pulmonary artery embolism derived from a tumor embolus was the suspected cause of the sudden change of the clinical course.