Aim: The aim of this study is to clarify the age-related characteristics of pediatric IgA nephropathy. Patients and methods: Five cases in preschool children less than 6 years old were analyzed and compared to 38 cases in older children from 6 to 15 years old. Results: The group of younger children had higher incidences of gross hematuria, hypertension, proteinuria, and hypoproteinemia. Renal biopsy specimens in this group showed more intracapillary lesions including mesangial cell proliferation and endocapillary proliferation of glomeruli, but less segmental lesions, global sclerosis, and interstitial changes. Conclusion: IgA nephritis in preschool children demonstrated more symptoms of acute onset and less chronic renal injury.