A 37-year-old woman was evaluated at our hospital for a treatment-resistant proctosigmoiditis. Fifteen years previously, ulcerative colitis was suspected and she was cured by steroid therapy. Colonoscopy revealed multiple sessile polyps covered with white exudate from the rectum to the sigmoid colon. Histopathological examination revealed a mucosal surface cover of granulation tissue. Based on these findings, cap polyposis was diagnosed. She underwent Helicobacter pylori eradication therapy, and at 1 month after therapy, her symptoms had improved. We present a case of cap polyposis relapsing 15 years after remission with steroid therapy, and that was improved by H. pylori eradication therapy.