Background: Sarcomatoid carcinoma of the ureter (SCU) is a highly aggressive and relatively uncommon malignant tumor of the urinary tract. Its frequency is quite low, and its prognosis is very bad when compared to other cancers of the urinary system. SCU clinical reports are still hard to come by. MRI and PEI/CT imaging of ureteral sarcomatoid cancer is presented in this case to promote diagnostic awareness and comprehension of the imaging characteristics of this uncommon illness. Method: The patient had ureteral sarcomatoid cancer, which was verified by pathological investigation after ureteroscopic biopsy. The patient’s clinical information, imaging results, surgical outcomes, and pathological findings were gathered. A retrospective study was carried out in combinationwith pertinent national and international literature. Results: An 84-year-old female patient was admitted for “left flank discomfort lasting over one month.” MRI revealed an irregular soft tissue mass in the middle-lower segment of the left ureter. T2-weighted imaging showed an unevenly slightly hyperintense signal. Diffusion-weighted imaging demonstrated restricted diffusion. Contrast-enhanced imaging exhibited heterogeneous enhancement. PET/CT demonstrated significantly increased fluorodeoxyglucose metabolism in the mass with secondary left upper urinary tract obstruction. Concurrent findings included a solitary metastatic lesion in hepatic segment S6 and multiple lymph node metastases along the left common iliac and external iliac arteries. Preoperative diagnosis suggested a malignant tumor of the ureter. The patient underwent left nephroureteroscopy with biopsy, and the postoperative pathological diagnosis was ureteral sarcomatoid carcinoma. Conclusion: Ureteral sarcomatoid carcinoma is a rare, highly malignant, and aggressive tumor with nonspecific imaging features, typically presenting as an invasively growing mass. Diagnosis relies on postoperative pathology and immunohistochemical examination. MRI and PET/CT scans are valuable for preoperative localization and characterization, tumor staging, treatment planning, and postoperative follow-up. The prognosis is extremely negative. The main treatment option is radical surgery, although constant monitoring is necessary since early recurrence and metastases are frequent after surgery.