A 62-year-old woman with inoperable lung cancer received systemic combined chemotherapy with cisplatin and vindesine sulfate. Lower extremity edema occurred after chemotherapy and an iliocavagram revealed a large intraluminal solitary thrombus, which was floating in the inferior vena cava (IVC) and extending up to the level of the renal vein. A thrombectomy using the simple IVC clamping procedure was successfully performed. Primary thrombosis of the IVC is rare, and this is the first reported case associated with lung cancer. A thrombectomy using the simple clamping of the IVC is considered to be a safe and effective procedure for the treatment of a free-floating thrombus in the IVC even in the case of a lung cancer patient.