Background/aim: After allogeneic hematopoietic stem cell transplantation (allo-HSCT), donor natural killer (NK) cells trigger alloreactions against potential recipient cells by their killer immunoglobulin-like receptors (KIRs). This study investigated whether KIR/HLA genotypes and KIR haplotypes of donors and recipients exhibit a critical function in the prevalence of acute graft-versus-host disease (aGVHD) and persistence of the graft after HLA-identical sibling allo-HSCT for patients with hematological malignancies. Materials and methods: We studied KIR and HLA genotypes in 115 related donors and recipients (56 patients with AML and 59 patients with ALL) who had received allo-HSCT from HLA-matched sibling donors. We evaluated 17 KIR genes and some alleles, including their ligands, using the PCR-SSP assay. Results: KIR gene frequency results between donors and recipients showed that donors had more activating KIR than their recipients. Chi-square comparison of KIR genotype frequencies in donors versus recipients revealed a significant difference (P < 0.001). We found a survival association between the donor lacking and the recipient having group B KIR haplotypes, although this was not statistically significant. Conclusion: This study suggests that we could exploit NK cell alloreactivity as a part of the optimization of donor selection and potential immunotherapeutic regimens to help facilitate good engraftment and reduce the risk of aGVHD incidence after allo-HSCT.