The patient, a 64-year-old woman, was diagnosed as having large cell carcinoma(stageIV)eighteen months ago. She received long-term chemotherapy, and her disease stabilized. She was admitted to our hospital with dyspnea and diagnosed with a pulmonary embolism by chest computed tomography(CT)and angiography of pulmonary artery. As a result of thrombolytic therapy and anticoagulant therapy, the thrombus decreased in size and her condition improved. Insertion of a vena cava filter and continuation of anticoagulant therapy were performed to prevent recurrence of PE. In this case, there were many prothrombogenic factors such as advanced malignancy, a long period of chemotherapy, corticosteroids, granulocyte-colony stimulating factor(G-CSF)and decreased physical activity. Thrombosis is a frequent complication in cancer patients and represents an important cause of morbidity and mortality. Great care should be taken for complications of thrombosis in cancer treatment.