INTRODUCTION: The role of tissue eosinophils and their relationship with interleukin-5 in gastrointestinal disorders have not been elucidated. This study aimed to analyze tissue eosinophils and interleukin-5 receptor-alpha subunit (IL-5RA) expression on eosinophils in inflammatory bowel disease (IBD). METHODS: Blood and stool test results and radiologic and endoscopic findings in pediatric patients, who were newly diagnosed with IBD, eosinophilic gastrointestinal diseases (EGIDs), or disorders of gut-brain interactions were retrospectively reviewed. Tissue eosinophil counts were analyzed, and immunohistochemistry was performed using an antibody against IL-5RA expressed on eosinophils in the colonic mucosa. RESULTS: The tissue eosinophil count and IL-5RA-expressing eosinophil density were significantly different among the three groups (P<0.005). IL-5RA expression was significantly higher in the IBD group than in the EGID group (P<0.001). In IBD, tissue IL-5RA expression was positively correlated with platelet count, erythrocyte sedimentation rate, and highly sensitive C-reactive protein, and negatively correlated with hemoglobin and albumin. In Crohn's disease (CD), higher IL-5RA expressions were observed with higher pediatric CD activity index (P<0.005). The optimal cut-off value for IL-5RA-expressing eosinophil density was 69.4/high-power field. DISCUSSION: The expression of IL-5RA in tissue eosinophils is elevated in treatment naive IBD. IL-5RA expression may reflect disease severity and its extent of involvement in early active CD.