Abstract: Objective To report a case of anaplastic sarcoma of the kidney (ASK) and improve the general understanding to this disease. Methods Clinical data about a patient with ASK admitted to the First Medical Center of Chinese PLA General Hospital in April 2019 were analyzed and related literatures were reviewed. Results The patient was a 20-month-old girl from Qingdao,Shandong province.She presented with gross hematuria during the process of urination,without dysuria,fever or other symptoms.Enhanced abdominal CT scan indicated a cyst in the lower pole of the right kidney.Right nephrectomy was performed under general anesthesia in other hospital on April 8,2019.The pathological diagnosis was anaplastic sarcoma of the kidney and its histological characteristics were widespread cellular anaplastic changes and chondrocyte differentiation without neoplastic epithelial structure,embryonic component or nephrogenic rests.Adjuvant chemotherapy was given routinely 3 weeks after surgery and 11 chemotherapy cycles had been completed.The patient survived uneventfully for more than one year,and the long-term prognosis required further observation and follow-up.It had been reported that most ASK patients of stageⅠ/Ⅱ could survive uneventfully for long time and stageⅢ/Ⅳ cases were more likely to have recurrence or metastasis after treatment. Conclusion Anaplastic sarcoma of the kidney is a rare pediatric tumor with unique pathological characteristics.Currently,there is no specific treatment plan for this rare tumor,and its prognosis may be related to neoplasm staging.