We present a case of primary ureteral carcinoma composed of both transitional cell carcinoma and mucinous carcinoma. A 79-year-old woman visited her home doctor with the chief complaint of right lower abdominal pain. Abdominal computed tomographic scan (CT) disclosed a tumor measuring about 5 cm in diameter at the right lower quadrant of the abdomen. Percutaneous nephrostomy was performed for hydronephrosis and pyonephrosis. The urinary cytology revealed class V, transitional cell carcinoma. Re-abdominal CT showed further enlargement of tumor diameter, but the primary site of the tumor was not identified. Her general condition worsened, and she died 42 days after her initial complaint. Pathologic examinations upon autopsy revealed both mucinous carcinoma and transitional cell carcinoma in the right ureter. Pathogenesis and management of this rare condition are discussed.