We report a case of squamous differentiated prostate carcinoma that developed after combination endocrine therapy for adenocarcinoma of the prostate. The patient was a 68-year-old man who visited our hospital with microscopic hematuria. His serum prostate-specific antigen (PSA) level was 7. 06 ng/ml. Transperineal needle biopsy was performed and histological examinations indicated moderately differentiated adenocarcinoma with a Gleason score of 4 + 4 = 8. Computed tomography showed swelling of left external iliac lymph node. The clinical stage was T3aN1M0. Six weeks after combination endocrine therapy using goserelin acetate and bicalutamide, the patient underwent radical prostatectomy and bilateral pelvic lymphadenectomy. Histopathological examination of the surgical specimen demonstrated squamous cell carcinoma of the prostate with very small areas of adenocarcinoma. The treatment measure was changed from endocrine therapy to combination chemotherapy consisting of docetaxel, cisplatin, and 5- FU. Eighteen month has passed after the surgery without any evidence of distant metastasis.