We report a case of pseudosarcomatous variant of transitional cell carcinoma of the renal pelvis which showed grossly and microscopically the distinct biphasic growth patterns. Grossly, most part of the tumor showed solid growth protruding into the renal pelvic cavity as well as infiltrating into the parenchyma of lower pole. The overlying pelvic mucosa was replaced by a diffuse, papillary transitional cell carcinoma, and the solid mass was composed of pleomorphic spindle cell sarcomatoid component with frequent myxoid change and a few foci of osteoid deposit. Ultrastructural study of the spindle cells revealed epithelial differentiation featured with rich cytoplasmic organelles, basal lamina and basement membrane-like structures, although immunohistochemistry failed to detect epithelial differentiation.