Allogeneic hematopoietic stem cell transplantation (HSCT) from HLA-matched donors is the gold standard. However, haploidentical stem cell transplantation using posttransplant cyclophosphamide (PTCY-haplo) and cord blood transplants (CBTs) are alternatives when HLA-matched donors are unavailable. Using the Japanese Registry data, we evaluated the impact of haploidentical donor age on posttransplant outcomes by comparing PTCY-haplo and CBT. We analyzed data for 5,161 patients aged 16-70 who received their first HSCT for acute leukemia, myelodysplastic syndrome, or chronic myeloid leukemia. Haploidentical donors were categorized as "younger" (<
40 years) or "older" (≥40 years), and the patients were divided into younger (<
50 years) and older (≥50 years) cohorts. In the older cohort, PTCY-haplo from younger donors had better overall survival (OS) (55.5% vs. 50.8%, P = 0.006), lower nonrelapse mortality (NRM) (17.3% vs. 28.6%, P <
0.001), and higher relapse rates (33.0% vs. 24.9%, P = 0.017) compared with CBT. PTCY-haplo from older donors had comparable OS (44.1% vs. 50.8%, P = 1.00), NRM (27.3% vs. 28.6%, P = 1.00), and relapse (29.2% vs. 24.9%, P = 0.90) to CBT. In the younger cohort, PTCY-haplo from younger and older donors showed comparable OS, NRM, and relapse to CBT. Compared to PTCY-haplo, cumulative incidence of acute graft-versus host disease (GVHD) was higher in CBT, regardless of donor age, in the older cohort. However, acute GVHD was lower in PTCY-haplo from younger donors in the younger cohort compared with CBT. PTCY-haplo from younger donors to older patients offers better clinical outcomes compared with CBT.