Allogeneic hematopoietic stem cell transplantation(allo-HSCT) is a curative therapy for severe aplastic anemia(SAA), with donor sources including matched sibling donors(MSDs), haploidentical donors(HIDs), and unrelated donors(URDs). However, the optimal criteria for donor selection remain undefined.We performed a multicenter retrospective study of 795 consecutive SAA patients who underwent alloHSCT between 2012 and 2020 across 11 transplant centers in China. The overall survival(OS), failurefree survival(FFS), and GVHD-free/FFS(GFFS) rates were 85.2%, 83.6%, and 76.1%, respectively. Donorrelated variables including relationship, age, sex match, blood type, and HLA mismatches were evaluated.Multivariable Cox regression identified donor age ≥50 years as an independent risk factor for inferior GFFS(HR = 2.13), OS(HR = 2.09), and FFS(HR = 2.18)(all P < 0.001). To directly compare the prognostic weight of donor age versus HLA compatibility, we stratified patients into four subgroups according to donor type(HID vs....