A case of vesico-appendiceal fistula caused by appendiceal cancer is reported. A 37-year-old male was admitted with the chief complaint of suspended dust in the urine. Under cystoscopy, a tumor (1 cm diameter) was found in the right posterior wall of the bladder. Transurethral resection of the bladder tumor was performed. The pathological outcome was intestinal metaplasia without malignancy. Preoperative abdominal computed tomography suggested vesico-appendiceal fistula, retrospectively. Therefore, appendectomy with partial cystectomy was attempted. However, the appendix was adhered to the sigmoid mesocolon, therefore, appendectomy, partial cystectomy, and sigmoid colectomy were performed. We diagnosed the tumor as mucinous adenocarcinoma. The patient has been receiving adjuvant chemotherapy with tegafur-gimeracil-oteracil potassium for 17 months, because he refused right hemicolectomy. There was no evidence of recurrence after 58 months of follow-up. Vesico-appendiceal fistula caused by appendiceal cancer is very rare. Our case is the 21st case reported in Japan.