A 54-year-old woman visited to a doctor nearby medical clinic complaining of loss of appetite. She was diagnosed with right hydronephrosis on abdominal ultrasonography, and referred to our hospital for further examination. Contrast abdominal computed tomography(CT)revealed that a 6.2 cm tumor with a contrast-enhancing effect inside in the retroperitoneum near the lower pole of the right kidney. She was diagnosed with hydronephrosis due to infiltration of the right kidney of a retroperitoneal tumor. The tumor was suspected of invading the duodenum and inferior vena cava, but no obvious lymph node or distant metastasis was observed. Abdominal MRI revealed a tumor showed hyperintensity on T2-weighted and diffusion-weighted images. We performed pancreaticoduodenectomy with inferior vena cava resection and right nephrectomy. The pathological diagnosis was leiomyosarcoma originating from retroperitoneum and pT2, pN0, pM0, pStage ⅢA. The postoperative course was good, and she was discharged 10 days after the operation. Thoracoabdominal CT showed a tumor 4 cm at the hepatic hilum three months after surgery, and EOB-MRI showed many tumors other than the same site, so multiple liver metastases were diagnosed as recurrence. Doxorubicin has been started and is still being treated.