Objective:To investigate the effect of Toll-Like receptor 4(TLR4) on the severity of acute graft-versus-host disease(GVHD) after haploidentical stem cell transplantation (HSCT) in mouse and explore its potential mechanism. Methods:Establish a mouse model of MHC haploidentical bone marrow transplantation. The mice were randomly divided into the experimental group 1(n=12):each mouse was received 20 μg/kg infusion of TLR4 agonist LPS; the experimental group 2(n=12):each mouse was received 20μg/kg infusion of TLR4 monoclonal antibody; the control group(n=12):six mice were received 20 μg/kg infusion of sterile saline; other six mice without any treatment after transplantation. We observed the clinical manifestation of GVHD and the survival rate by using Kaplan-Meier analysis. On the 14th day after transplantation,the histopathology of GVHD was evaluated in the liver,and the change of serum IL-1β,TNF-α was detected. Results:Compared with the control group,the mice in the experimental group 2 had reduced severity of acute GVHD symptoms,improved survival rate(P < 0.05) and less histopathological evidence of GVHD. Correspondingly,the above changes of the mice in the experimental group 1 were severe. Conclusion:The TLR4 inhibitors can prevent acute GVHD in murine haplo-HSCT model.