A 63-year-old Japanese man with a 1-month history of dyschezia and dysuria was referred to our hospital. Transrectal ultrasonography and magnetic resonance imaging demonstrated a mass involving the prostate, measuring about 6.5 cm. The serum prostate specific antigen was 20.3 ng/ml. By the transperineal needle biopsy, it was suspected to be fibrosarcoma. Total pelvic exenteration was performed. Histopathological examination of the tumor revealed carcinosarcoma of the prostate. One month after the operation local recurrence was manifested by perineal pain. The recurrent tumor grew rapidly with severe pain. The patient's condition deteriorated, and finally he died of the disease nine months after the operation. Carcinosarcoma of the prostate is a rare neoplasm and very aggressive. There is no established protocol for its treatment and its prognosis is usually poor. This is the 49th case reported in the literature.