We report a case of angiosarcoma complicated by bilateral massive bloody pleurisy (hematocrit of 7.2%) in an 83-year-old woman. An autopsy revealed hemorrhagic tumors infiltrating both the diaphragm and serosal surface of the peritoneum. Histological examination confirmed an anastomosing vascular channel pattern of the tumor cells with characteristic immunohistochemical findings for angiosarcoma, such as positive staining for vimentin, CD31, CD34, D2-40, and factor VIII-related antigen. The tumor was thought to have originated from a small vessel on the serosal surface of the duodenum. We also reviewed cases of hemothorax associated with angiosarcoma, which suggested that primary or metastatic pleural angiosarcoma should be considered a cause of spontaneous hemothorax, especially in patients with bilateral and/or intractable hemothorax.