A 59-year-old man was referred to us for evaluation of asymptomatic mass in the liver that had been detected on ultrasonography performed during a physical screening. He had no history of hepatitis, and was otherwise well. Tumor markers were normal, including alpha fetoprotein, carcinoembryonic antigen, neuron-specific enolase and cancer antigen 199. Abdominal CT showed a 5.0 cm diameter low density mass in the S6 segment of his liver, with mild peripheral enhancement. Abdominal MR demonstrated the mass with hypointensity on T1WI, inhomogeneous hyperintensity on fat-suppressed T2WI, and mild peripheral enhancement. Partial hepatectomy was performed and pathological examination indicated undiferentiated pleomorphic sarcoma, with immunohistochemical results as follows: Vimentin (+), CK (-), CD68 (+), INI-1 (+), Hepa (-), Gly-3 (-), Arg-1 (-), HMB45 (-), CAM5,2 (-), CD31 (-), CD34 (-), CK7 (-), CK19 (-),Desmin (-), SMA (+), EMA (-), S-100 (-), Ki67 (50%+). The patient underwent postoperative chemotherapy with karelizumab and gemcitabine. However, repeat MR 3 months later showed multiple nodules with rim-like enhancement around the surgical margin. Subsequent repeat CT 6 months later reveled marked progression of the lesions.