We report a case of primary undifferentiated small cell carcinoma of the ureter. A 62-year-old man showed gross hematuria. Retrograde pyelography and CT scan revealed a tumor in the left ureter. The light microscopic examination revealed small cell carcinoma and transitional cell carcinoma. To the best of our knowledge, this is the first report of a small cell carcinoma originating in the ureter in Japan.