BACKGROUND: While three Janus kinase inhibitors (JAKi) have demonstrated efficacy in ulcerative colitis (UC), scarce data exist regarding JAKi intraclass switching. AIM: To evaluate the effectiveness and safety of a second JAK inhibitor in UC. METHODS: This was a multicentre, retrospective, observational cohort including patients with moderate to severe UC who received a second-line of JAKi after failure or intolerance of a first. The primary outcome was steroid-free clinical remission (SFCR) at Weeks 8-14, defined as a partial Mayo score of 2 or less with no individual sub-score above 1. RESULTS: Among the 169 patients from 28 participating centres, 105 received upadacitinib, 54 filgotinib and 10 tofacitinib as a second-line of JAKi. Overall, 81/169 achieved SFCR at Weeks 8-14: 58/105 with upadacitinib, 18/54 with filgotinib and 5/10 with tofacitinib (p = 0.03). In the multivariate analysis, upadacitinib was independently associated with higher odds of SFCR than filgotinib (OR = 3.15, 95% CI [1.52-6.79]). With a median follow-up duration of 96 days, drug persistence at 6 months was 72.8% with upadacitinib, 57.2% with filgotinib and 66.7% with tofacitinib (p = 0.099). 24.3% of patients (41/169) experienced at least one adverse event leading to treatment withdrawal in 9 patients (5%). No cases of death, cancer, or major acute cardiovascular events were reported. CONCLUSION: A second-line of JAKi provided clinical remission in about half of patients after induction, and was well tolerated.