Background & Aims: The relatively high cost and patent expiry of infliximab (IFX), an anti-tumor necrosis factor monoclonal antibody used in inflammatory bowel disease (IBD), has led to the development of biosimilar versions of the reference product (RP). The biosimilar CT-P13 has been approved worldwide for all indications held by the infliximab RP. This study investigated the long-term efficacy, safety, pharmacokinetics, and immunogenicity of CT-P13 after switching from infliximab RP. Methods: In this prospective, observational study, patients with pediatric-onset IBD receiving maintenance IFX RP were followed for one year after continuing IFX RP (RP maintenance group) or switching to CT-P13 (CT-P13 switch group). Primary endpoints were the proportion of patients continuously receiving infliximab and the proportion achieving persistent remission – corticosteroid-free sustained clinical remission without dose intensification – at one year. Clinical activity scores, laboratory test results, IFX trough levels, and antibody to IFX levels were also compared between groups, and also between switch point and 1 year after in the CT-P13 switch group. Results: Seventy four patients (64 patients with Crohn\'s disease, 14 patients with ulcerative colitis) were included in this study. Thirty-six patients were recruited to the RP maintenance group and 38 to the CT P13 switch group. In the maintenance and switch group, 31 (86.1%) and 35 (92.1%) patients continuously received IFX for one year ( P = 0.649), and 24 (77.8%) and 28 patients (78.9%) experienced persistent remission at one year ( P =1.000), respectively. There were no statistically significant differences in any measures of disease activity, pharmacokinetics, or immunogenicity between the two groups at 1 year as well as between the time of switch and 1-year post-switch in the CT-P13 switch group. Twenty-seven adverse events occurred in the maintenance group and 30 in the switch group. No serious adverse events or infusion-related reactions leading to discontinuation of IFX were observed. Conclusions: Switching from maintenance IFX RP to CT-P13 did not result in any significant differences in efficacy, pharmacokinetics, or immunogenicity in patients with pediatric-onset IBD and no unexpected safety issues occurred, supporting findings from randomized controlled trials.