Undifferentiated embryonal sarcoma of the liver (UESL) is rare in adults, and its clinical manifestations, laboratory tests, and imaging findings lack specificity. Diagnosis relies on pathological diagnosis. This article reports a 55-year-old male patient with UESL who was admitted to the hospital due to right upper abdominal pain for 3 months. He had no history of chronic hepatitis or cirrhosis, and the tumor marker was only elevated CA-125. CT showed a huge cystic solid exogenous mass in the right lobe of the liver. The patient underwent right hemihepatectomy due to tumor rupture and bleeding. Postoperative pathology confirmed UESL, and genetic testing revealed FGFR2 amplification and TP53 mutation. This disease needs to be differentiated from hepatocellular carcinoma and liver abscess. Surgical resection is the preferred treatment, and postoperative combined chemotherapy can effectively improve prognosis.