An 82-year-old woman was admitted to our hospital with a palpable mass in her right lower abdomen. The mass was enlarged and tender for the previous 3 months. Abdomen-pelvic computed tomographic scan demonstrated severe right hydroureteronephrosis and about an 8x8x9cm sized huge irregular shaped pelvic mass. Retrograde pyelography showed complete obstruction of the right middle ureter. En bloc resection of the mass and segmental resection of the ureter was performed. Pathologically, it was diagnosed primary leiomyosarcoma of the ureter. At 3 month postoperatively, there has been no recurrence or metastasis.