A case report of left renal cell carcinoma with tumor thrombus extending into the right atrium is reported. A 76-year-old woman was found to have a left renal tumor with tumor thrombus extending into the inferior vena cava and right atrium by computed tomographic-scanning. Left nephrectomy and removal of an intra-atrial tumor thrombus were performed under a cardiopulmonary bypass. The post-operative course was uneventful and the patient was discharged from the hospital 22 days postoperatively. The pathological diagnosis was clear cell carcinoma. After surgery, the patient received interferon-gamma. However, the patient developed lung metastases 26 months after the operation and is currently being observed while receiving interferon-alpha.