AbstractThe algorithm for cord blood (CB) unit selection is still somewhat ambiguous. We retrospectively analyzed 620 cases of acute leukemia between 2015 and 2020, who were treated with myeloablative single‐unit umbilical CB transplantation (UCBT). We found that, when human leukocyte antigen (HLA) mismatch was ≤3/10, CD34+cell dosage <0.83 × 105/kg—considerably lower than prevalent guidelines—was permissible without affecting survival. Moreover, synergy between donor killer‐cell immunoglobulin‐like receptors (KIR) haplotypes‐B and donor‐recipient HLA‐C mismatch protected against relapse‐related mortality. We submit that minimum required CD34+cell dosage can possibly be relaxed to broaden access to UCBT, and donor KIR genotyping should be considered during unit selection.