Abstract A 72-year-old man complaining of upper abdominal discomfort was diagnosed as having retroperitoneal liposarcoma by means of diagnostic imaging. He then underwent an operation. One mass existed on the curvatura ventriculi major, extending to the hilum splenicum and pressing back the pancreal head and body. There was another mass to the left of the first, situated on the ventral side of the left kidney. Also, another mass was intramurally found adjacent to the curvatura ventriculi major. Histologically, the mass on the curvatura ventriculi major ranged from the peritoneal cavity to the retroperitoneum Its intraperitoneal portion was classified as a differentiated lipoma-like type and the retroperitoneal mass was of mucous type. The mass on the left kidney was of a differentiated fibrosing type. The intramural mass in the gastric curvature was found to be a differentiated lipoma-like type. The patient has been under observation for 12 months and has shown no recurrence.