To explore the effect and pathogenssis of acute graft-versus-host disease (aGVHD) on early diffuse lung injury in allogeneic hematopoietic stem cell transplantation (allo-HSCT), we established an aGVHD model of C(57)BL/6-->BALB/c mice. Chest computed tomography (CT) scans, histopathology and the levels of cytokines including tumor necrosis factor alpha (TNFalpha) and Interferon (IFNgamma) in lungs were dynamically detected in recipient mice after transplantation. The incidence of aGVHD was respectively 0%, 0% and 100% in simple irradiation group (A), syngeneic transplant group(B) and allogeneic transplant group (C). Chest CT scans of recipient mice were normal in 3 groups on days +3 and +7 after transplantation. CT showed that two of ten mice had bilateral lung diffuse infiltrate on day +12 (on the brink of death) in group A and 6 of 10 mice had bilateral lung diffuse infiltrate on day +14 (3 d after aGVHD occurring) in group C, and were normal on days +12 and +14 in group B after transplantation. Histopathology of lungs in the 3 groups was similar, consisting of minor interstitial pneumonitis on day +3. Group A showed edema, hyperplasia of epithelial cells and widened alveolar interval on day +7, and epithelial cell necrosis, lymphocyte infiltration, hemorrhage, protein leakage, and local consolidation on day +12. The histopathology of group B showed slight edema of epithelial cells on +7 day, which were slighter than that on day +3, and virtually normal on day +14. The histopathology in group C was characterized by the significant expansion and congestion of capillaries, and lymphocyte infiltration on day +7, the acute pneumonitis was present involving tissue edema, lymphocyte and macrophage infiltration, protein leakage and perivascular inflammation on day +14. In group A, the levels of TNFalpha were lower on day +7 than on day +3. In group B, the levels of TNFalpha attained a peak on day +3, which decreased on days +7 and +14. In group C, the levels of TNFalpha were highest on day +7 and there was a significant difference between those on days +7 and +14 (P=0.816). In group A, the levels of IFNgamma on day +7 were higher than on day +3. In group B, the levels of IFNgamma increased progressively, but the comparison of IFNgamma levels in different times had no statistical significance (P=0.521, 0.118, 0.340). In group C, the levels of IFNgamma attained a peak by day +7 and decreased on day +14. aGVHD is the main cause of early non-infectious lung injury. T lymphocytes and TNFalpha are possibly implicated in the pathogenesis of acute GVHD-induced lung injury. The decreased levels of IFNgamma in lung tissues following transplantation might be associated with pulmonary fibrosis in late non-infectious pulmonary complications.