A 42-year-old woman presented with left renal tumor. Computed tomography showed a left renal tumor (6 cm in diameter) and a tumor thrombus at the left renal vein, which had equal density to fat tissue. She was diagnosed with malignant tumor, and underwent radical left nephrectomy and resection of thrombus. Pathological diagnosis was angiomyolipoma with no findings of malignancy. No signs of recurrence or metastasis have been observed for 8 months after the operation.