Undifferentiated embryonal sarcoma of the liver (UESL) is a rare adult neoplasm. The primary treatments for UESL are total surgical resection and adjuvant multiagent chemotherapy. The current study presents a case of UESL in a 9-year-old female with abdominal pain and fever as her first symptoms. A cystic mass with solid components was discovered on sonography and computed tomography (CT) imaging. The patient underwent tumor removal surgery in addition to a liver lobectomy on the right side. The pathologist reported a single-focal cystic solid mass confined to the liver with no capsular invasion, and the final diagnosis based on the immunohistochemistry (IHC) results was UESL. The patient received chemotherapy, and she is doing well eight months after surgery with no signs of recurrence. In conclusion, large cystic hepatic lesions should be considered in the differential diagnosis. Despite the poor prognosis of UESL, aggressive surgical resection should be the most important factor in ensuring long-term survival.