OBJECTIVE : Tacrolimus is very effective at inducing remission in patients with refractory ulcerative colitis. However, the optimal time-point for the discontinuation of tacrolimus is controversial because administration of tacrolimus for > 3 months is currently not approved for insurance reimbursement in Japan. We conducted this study to determine the optimal time of discontinuation of tacrolimus in patients with ulcerative colitis. METHODS : Of 38 patients who received tacrolimus as remission induction therapy for refractory active ulcerative colitis between 2009 and 2018, this study included 21 patients who received tacrolimus for ≥ 3 months before being switched to thiopurines. These patients were divided into two groups for analysis: the confirmed switch (CS) group (n = 13), in which tacrolimus was switched to azathioprine after endoscopic confirmation of mucosal improvement, and the mandatory switch (MS) group (n = 8), in which tacrolimus was switched to a thiopurine agent without endoscopic confirmation of improvement. RESULTS : The relapse rates after the switch to azathioprine were 23% and 88% in the CS and MS groups, respectively (p = 0.0075). No patient of the CS group underwent surgery, while 50% of patients of the MS group underwent surgery (p = 0.0117). The cumulative event-free rates at 6 months, 1 year, and 2 years were 92%, 92%, and 65%, respectively, in the CS group and 15%, 15%, and 0%, respectively, in the MS group (p < 0.0001). The incidence rate of adverse reactions was 31% in the CS group and 13% in the MS group, but there were no serious adverse reactions. CONCLUSIONS : It seems preferable to discontinue tacrolimus after endoscopic confirmation of mucosal healing. However, attention should be paid to the potential occurrence of adverse reactions associated with long-term tacrolimus therapy.