To investigate the relationship between the plasma levels of chemokine CXCL9/Mig and acute graft-versus-host disease (aGVHD) after allogeneic hematopoietic stem cell transplantation (allo-HSCT). The plasma levels of CXCL9/Mig of 35 patients who received all-HSCT were detected by using ELISA assay, these patients included 13 patients with grade 0-I, 12 patients with grade II and 10 patients with grade III - IV aGVHD, respectively. The four different time points including prior to allo-HSCT, one week before aGVHD onset, the plateau of aGVHD and time after completely controlled, were studied. The results showed that the plasma levels of CXCL9/Mig in the patients with serious aGVHD (grade II - IV) were significantly increased during aGVHD than those in the patients without aGVHD or with slight aGVHD (P < 0.001). It was found that CXCL9/Mig levels were significantly correlated with the severity of grade aGVHD (P < 0.001). Another important finding was that CXCL9/Mig levels obviously increased at one week before aGVHD was diagnosed. CXCL9/Mig level was not obviously correlated with CMV infection or other infectious complication (P > 0.05). It is concluded that the plasma level of CXC19/Mig significantly correlated with the severity of aGVHD and plays a critical role in pathogenesis of aGVHD, the changes in plasma level of CXCL9/Mig after allo-HSCT may be used as a valuable indicator for early diagnosis of aGVHD, finally, provide a early therapeutic approach to reduce aGVHD severity and improve the outcome for patients after allo-HSCT.