Abstract: Objective To explore the correlation between endothelial activation and stress index (EASIX) and the severity and prognosis of acute graft-versus-host disease (aGVHD) following allogeneic hematopoietic stem cell transplantation (allo-HSCT).Methods Retrospective analysis was conducted using clinical data from 87 patients with acute myeloid leukemia (AML) who underwent allo-HSCT at the Affiliated Hospital of Xuzhou Medical University from January 2016 to December 2021. The relationship between pre-treatment EASIX (EASIX-pre) and the severity of aGVHD was analyzed, and the impact of EASIX-pre on overall survival (OS) and relapse-free survival (RFS) was evaluated.Results Receiver operating characteristic (ROC) curve analysis showed that EASIX-pre had good predictive value for aGVHD severity, with a cutoff value of 6.19. Compared with the EASIX-pre≤6.19 group, the EASIX-pre>6.19 group showed a higher likelihood of developing grades 2-4 aGVHD (cumulative incidence, 14.58% vs. 56.25%, P<0.001). The median OS (54 months vs. not reached, P=0.013) and median RFS (47 months vs. not reached, P=0.010) were significantly worse in the EASIX-pre>6.19 group, with statistical differences (P<0.05). According to multivariate Cox regression analysis, EASIX-pre is an independent risk factor influencing OS and RFS in AML patients after allo-HSCT.Conclusions EASIX-pre is useful in identifying the severity of aGVHD in AML patients following allo-HSCT. EASIX-pre serves as an independent adverse prognostic factor for OS in these patients.