Objective: To explore the impact of the natural killer cell immunoglobulin-like receptor/human leukocyte antigen (KIR/HLA) receptor-ligand model in single unrelated cord blood transplantation (sUCBT) . Methods: Between July 2012 and June 2018, 270 patients with malignant hematologic diseases receiving single-unit UCBT were divided into two groups. Group 1 (n=174) patients lacked a C-ligand for inhibitory KIR on UCB NK cells (patients homozygous C1/C1 or C2/C2) . Group 2 (n=96) patients expressed both C ligands for inhibitory KIR in the receptor (patients heterozygous C1/C2) . Results: A total of 270 patients (146 males, 124 females) with a median age of 13 years (1-62) were included in this retrospective study. All patients received a myeloablative conditioning regimen (without ATG) . The ratio of neutrophil engraftment for group 1 and 2 were both 98.9%, the median time of neutrophil engraftment for group 1 and 2 was 16 (10-41) days vs 17 (11-33) days (P=0.705) . The ratio of platelet engraftment was 88.5% for group 1 and 87.5% for group 2, the median time of platelet engraftment was 35 (11-113) days vs 38.5 (13-96) days (P=0.317) . The cumulative incidence of Ⅱ-Ⅳ acute GVHD in 100 days was 38.7% (95%CI 31.4%-45.9%) for group 1 and 50.0% (95%CI 39.6%-59.6%) for group 2 (P=0.075) , but multivariate analysis showed that HLA-C ligand absence was an independent protective factor for Ⅱ-Ⅳ acute GVHD after transplantation (P=0.036) . Patients in absence of a C-ligand for inhibitory KIRs (Group 1) showed a lower relapse rate than patients with both C-ligands (group 2) : 17.7% (95%CI 11.7%-24.9%) vs 22.7% (95%CI 4.4%-32.2%) after 3 years (P=0.288) . The median follow-up time was 742 (335-2 512) days. The 3-year OS was 72.1% for group 1 and 60.5% for group 2 (P=0.079) . There was no statistically significant difference between the two groups in 3-year disease-free survival [64.9% (95%CI 56.2%-72.3%) vs 55.4% (95%CI 44.4%-65.0%) (χ(2)=3.027, P=0.082) ]. Non-relapse mortality for group 1 was 12.1% (95%CI 7.7%-17.4%) and for group 2 was 16.7% (95%CI 10.0%-24.8%) (P=0.328) . Conclusion: Patients lacking a KIR-ligand of HLA group C1 or C2 had a lower incidence of grades Ⅱ-Ⅳ acute GVHD after sUCBT.