Sudden chest pain, dyspnea, and tachypnea occurred in a 21-year-old female who was undergoing induction chemotherapy under a diagnosis of minimally differentiated acute leukemia (M0). The arterial blood gas (ABG) tensions were decreased (PO2 71.6 mm Hg, PCO2 23.7 mm Hg), and an electrocardiogram showed a right-bundle branch block. Coagulation abnormalities (PT 73.1%, APTT 39.4 s, FDP 235mg/dl) were observed 72 h before onset. Echocardiography revealed a large thrombus in a right ventricle. A diagnosis of pulmonary thromboembolism (PTE) was made, and a tissue-type plasminogen activator (monteplase) was administered under percutaneous cardiopulmonary support (PCPS). The complete lysis of thrombus was confirmed by an echocardiogram 8 h later. Symptoms and ABG data were also improved. PTE in adult AML cases is rare, but should be considered as one of the life-threatening complications in AML patients under chemotherapy who develop respiratory difficulties. We suggest a careful monitoring of coagulation abnormalities for the prediction of PTE during chemotherapy for AML, and the use of tissue-type plasminogen activator (t-PA), monteplase, for the treatment of PTE in these cases.