A 52-year-old house wife presented with pain on urination. Cystoscopy and magnetic resonance imaging revealed solid and sessile tumor of 3 cm in diameter invading the bladder wall. Pathological examination of the transurethral resection specimen showed proliferation of spindle cells and epithelial cells. Since both types of cells were positive for cytokeratin immunostaining, sarcomatoid carcinoma was highly suspected. She underwent anterior pelvic exenteration and construction of continent reservoir (Penn Pouch). Since the tumor cells showed spindle cell proliferation alone without epithelial growth and positive staining for anaplastic lymphoma kinase, we corrected the final diagnosis as an inflammatory myofibroblastic tumor of the urinary bladder. She has been doing well without recurrence for 1 year.