Background: Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a curative therapy for pediatric hematologic malignancies. ABO blood group incompatibility is common in pediatric transplantation because of limited donor availability, but its impact on survival outcomes and hematopoietic recovery remains controversial. Objective: To compare transplantation outcomes between ABO-compatible and ABOincompatible allo-HSCT in children and to evaluate the effects of different types of ABO incompatibility. Methods: We retrospectively analyzed pediatric patients with hematologic malignancies who underwent allo-HSCT at the Children’s Hospital of Soochow University between October 2010 and January 2025. A total of 561 patients were included, comprising 298 ABO-incompatible and 263 ABO-compatible transplants. The primary outcome was overall survival (OS). Secondary outcomes included neutrophil and platelet engraftment, acute graft-versus-host disease (aGVHD), and viral reactivation, including Epstein–Barr virus (EBV) and cytomegalovirus (CMV). Results: Among the 561 patients, there was no significant difference in 3-year OS between the ABO-compatible and ABO incompatible groups (P > 0.05). The median time to neutrophil engraftment was shorter in the ABO-compatible group than in the ABO-incompatible group (12.7 [12.3–13.2] vs. 13.5 [13.0–14.0] days, P < 0.05). Median platelet engraftment time did not differ significantly (P > 0.05). The incidence of grade II–IV aGVHD was comparable between groups (P > 0.05), as were EBV and CMV reactivation rates (P > 0.05). Conclusion: ABO compatibility was associated with earlier neutrophil engraftment, whereas ABO incompatibility did not adversely affect engraftment, major complications, or survival in pediatric allo-HSCT.