Primary renal sarcoma is extremely rare and account for less than 1% of malignant renal tumors. We report a 24-year-old female with huge undiffer- entiated sarcoma arising from renal parenchyma of left kidney. The tumor was confined in the renal cortex without disruption of the renal capsule, which was difficult to be differentiated from renal cell carcinoma due to its unusual location. We pre- sent the imaging and histopathological findings of this rare case, and review the literatures. Primary renal sarcoma is a very high grade malignant tumor with various subtypes. The various mesenchymal cells found in the kidney may potentially develop into tumors of different histology. Leiomyosarcoma, fibrosarcoma, and liposarcoma are most frequent malignant ones. Most of the primary renal sarcoma arises from renal capsule or renal sinus. Undifferentiated sarcoma arising from renal parenchyma is extremely rare. We reported a 24-year- old female with a huge undifferentiated renal sarcoma arising from renal cortex with blood supply from renal artery. The pre-operative diagnosis of this unusual tumor was challenging because of its atypical imaging findings on both CT and angiography. The accurate diagnosis strongly depends on histopathologic findings. Despite of its rarity, primary renal sarcoma should be taken into differential diagnostic considera- tions in huge renal tumors.