A total of 1325 UC patients with oral 5-ASA maintenance therapy were identified. We excluded 661 patients who received thiopurines (6-mercaptopurine and azathioprine), anti-TNF-α agents (adalimumab and Infliximab), tacrolimus, and topical treatment such as a suppository or enema, and 87 patients who had a pMayo score of ≥ 2 at the start of the observation period. Among 577 patients, 50 patients with pMayo score of 2 at least once during observation period were excluded. Consequently, 527 patients were included in this study. Of these, 300 received a high dose of 5-ASA and 227 received a low dose. Ninety patients (30.0%) in HDG and 47 patients (20.7%) in LDG relapsed. The difference in relapse rates between HDG and LDG was statistically significant (p = 0.016).