A 82-year-old man was referred to our hospital with a chief complaint of macrohematuria and pollakisuria. Cystoscopy showed an abnormal mucosa on the right wall. We suspected carcinoma in situ but two months after cystoscopy showed a non-papillary and sessile tumor with calcification. We performed transurethral resection of the bladder tumor, muscle layer and adipose tissue. Histopathological findings revealed small cell carcinoma of the bladder infiltrating the externaladipose tissue. As postoperative adjuvant therapy, chemotherapy (cisplatin total 150 mg) was performed with 40 Gy of extra beam radiotherapy to the bladder. After chemotherapy and radiotherapy,urinary cytology was negative and cystoscopy showed the scar. Follow up magnetic resonance imaging revealed disappearance of the bladder tumor.