Rationale: Tofacitinib is an orally administered selective Janus kinase inhibitor. Its efficacy and safety in adults with moderately to severely active ulcerative colitis (UC) have been evaluated in clinical trials; however, its efficacy in pediatric patients with UC is limited.Patient concerns: A 9-years-old boy was referred to our hospital with chief complaints of diarrhea and bloody stool for 2 months. Colonoscopy revealed total colitis-type UC. His pediatric UC activity index score was 40, indicating moderately active UC.Diagnosis: UC.Interventions: Vedolizumab, golimumab, and ustekinumab were introduced because of steroid-resistant refractory UC; however, none of these biologics were effective or the effect was short-lived. Therefore, tofacitinib was administered 5 mg twice a day.Outcomes: The patient achieved UC remission after tofacitinib treatment, leading to maintained remission without adverse events.Lessons: To the best of our knowledge, this is the first pediatric case of moderately active UC that was successfully treated with tofacitinib in Japan. Tofacitinib is a safe drug for pediatric patients with moderately active UC. Even in steroid-dependent cases refractory to other biologics, tofacitinib can result in remission induction and maintenance effects. In children and adults, high-dose tofacitinib during induction therapy may be unnecessary to reduce adverse events.Abbreviation: AEs = adverse events, JAK = janus kinase, NR = normal range, PUCAI = pediatric ulcerative colitis activity index, TCS = total colonoscopy, UC = ulcerative colitis, UCEIS = ulcerative colitis endoscopic index of severity.