We report a case of undifferentiated (embryonal) sarcoma of the liver (UESL), which showed cystic formation in a 20-year-old man with no prior history of any hepatitis or liver cirrhosis. He was admitted with abdominal pain and a palpable epigastric mass. The physical examination findings were unremarkable except for a tenderness mass and the results of routine laboratory studies were all within normal limits. Abdominal ultrasound and computed tomography (CT) both showed a cystic mass in the left hepatic lobe. Subsequently, the patient underwent a tumor excision and another two times of hepatectomy because of tumor recurrence. Immunohistochemical study results showed that the tumor cells were positive for vimentin, alpha-1-antichymotrypsin (AACT) and desmin staining, and negative for alpha-fetoprotein (AFP), and eosinophilic hyaline globules in the cytoplasm of some giant cells were strongly positive for periodic acid-Schiff (PAS) staining. The pathological diagnosis was UESL. The patient is still alive with no tumor recurrence for four months.