Anticoagulation in venous thrombosis associated with Behçet disease (BD) is controversial. We herein report a 47-year-old woman with vessel thrombosis and pulmonary artery aneurysm (PAA) associated with BD who died of massive hemoptysis under oral anticoagulant. Although she was initially diagnosed with oral contraceptive-induced venous thromboembolism, a subsequent investigation led to a diagnosis of BD. Follow-up computed tomography (CT) showed persistent thrombus, so anticoagulant was continued for persistent thrombus. She died of massive hemoptysis after the development of PAA was identified on follow-up CT during the period of anticoagulation. Great care to prevent bleeding events is required when administering anticoagulants for BD with vessel thrombosis.