We report 2 cases of retroperitoneal liposarcoma. Case 1: A 53-year-old woman with severe abdominal distension and dyspnea was admitted to our hospital. Abdominal computed tomography(CT) and magnetic resonance imaging(MRI) revealed a large mass that occupied almost the entire abdominal cavity. She underwent surgery under the diagnosis of retroperitoneal liposarcoma. The tumor originated from the left lower pelvis. The tumor weighed 18 kg, and the histopathological diagnosis was well-differentiated liposarcoma. Seven years after the operation, local recurrence was found without any complaints. The operation was performed again. The tumor weighed 750 g, and it originated from the same area as observed in the first operation. The histopathological diagnosis was well-differentiated liposarcoma. Case 2: An 82-year-old woman complained of abdominal distension. A new dumbbell-like solid tumor was identified as retroperitoneal liposarcoma by CT and MRI findings, and it was growing rapidly. The tumor was removed with the cecum and right kidney in a curative operation. The tumor weighed 2.6 kg, and the histopathological diagnosis was dedifferentiated liposarcoma. The best treatment for retroperitoneal liposarcoma is curative resection. However, dedifferentiation occasionally occurs over time and in recurrent cases. It is important to follow-up strictly for retroperitoneal liposarcoma.