A 78-year-old man underwent surgery to remove a bladder tumor. The bladder contained two solid pedunculated tumors, which existed independently. Histopathologic examination revealed that of most the tumor was composed of spindle-shaped sarcomatous tissue sometimes containing multinucleated giant cells. Transitional cell carcinoma (Grade 3) was also found at the stalk of the tumor with squamous metaplasia. The squamous metaplasia, which gradually changed into sarcomatous tissue, was also found at many parts of the tumor, but no definite transition of the transitional cell carcinoma into sarcomatous tissue was noted. Therefore, the sarcomatous change of carcinoma in our case was brought about by way of squamous metaplasia of transitional cell carcinoma. The tumor could be given the diagnosis of so-called "carcinosarcoma". The pathologic significance of "carcinosarcoma" was briefly discussed.