The predictive factors for the development of pouchitis after ileal pouch-anal anastomosis (IPAA) in pediatric-onset ulcerative colitis (UC) have not been well investigated. The present study aimed to determine the predictive factors for the development of pouchitis after IPAA in the pediatric UC population. The data from 54 patients with pediatric-onset UC who underwent IPAA in Mie University Hospital between 2000 and 2017 were retrospectively reviewed. A modified pouchitis disease activity index of ≥5 was defined as pouchitis. Potential preoperative, intraoperative, and postoperative predictors for pouchitis including various demographic and clinical variables were analyzed using Cox regression analysis, Students' t-tests, Mann-Whitney U tests, and Kaplan-Meier curves. The optimal cutoff value for continuous variables was determined using the receiver operating characteristic curve analysis. Pouchitis was identified in 17 (31.5%) patients within 5 y of follow-up. In multivariable analysis, the independent predictors for pouchitis were preoperative cumulative steroid dose of >10,000 mg (P = 0.0056) and >65% neutrophils just before IPAA (P = 0.032). Multivariate analysis revealed that the independent predictors of pouchitis were a total steroid dose of >10,000 mg (P = 0.0002) and a neutrophil percentage of >65% (P = 0.0078). No patient for whom both of these independent predictors were negative developed pouchitis, whereas >40% of patients who had one or both predictors developed pouchitis. In pediatric patients with UC, the predictive factors for pouchitis development are a greater cumulative total dose of steroids and a greater percentage of neutrophils before IPAA.