Malnutrition during the peri-transplantation period is known to result in negative outcomes after allogeneic hematopoietic cell transplantation (allo-HCT). The nutritional risk index (NRI) which is a simple index calculated using serum albumin levels and body weight (BW) ratio (current BW/ideal BW) has been reported be to a prognostic factor in adult HCT. However, its usefulness in pediatric HCT setting remain unclear. Therefore, we retrospectively analyzed the impact of the NRI before allo-HCT on outcomes in pediatric patients. We found that poor nutritional status before pediatric HCT led to a worse prognosis, including NRM.