Primary signet-ring cell carcinoma of the urinary bladder is extremely rare and patient survival is very poor. The disease usually presents at advanced stages because the cancer progresses rapidly. The only option for effective treatment is radical cystectomy, and no effective chemotherapy has been established for this variant. We report a case of signet-ring cell carcinoma of the urinary bladder with a long-term survival of 90 months owing to radical cystectomy and combination adjuvant chemotherapy with S-1 and cisplatin. To our knowledge, this is the first report to demonstrate the long-term therapeutic activity of combination S-1 and cisplatin adjuvant chemotherapy against invasive signet-ring cell carcinoma of the urinary bladder.