Graft versus host disease (GVHD) is a life threatening complication of bone marrow stem cell transplantation, in which considerable numbers of proinflammatory cytokines secreted by allo-reactive donor T cells are involved. We and other previous studies have found that interleukin-22 (IL-22) was able to aggravate the target organs damage of GVHD. However, the mechanism and the signal pathway of IL-22 in murine acute GVHD was not clear. Here, we observed that compared with GVHD group, more serious pathological damage and more CD3⁺ T cells infiltrated in GVHD target organs were detected in the mice injected with IL-22. Meanwhile, transcription factor T-bet, RORγt and AhR respectively associated with Th1, Th17 and Th22 cells changed in varying degrees in different GVHD target organs. Furthermore, the increased expression of IL-22R and its downstream protein P-STAT3 were detected in GVHD mice with IL-22 treated. These results suggested that the pathological role of IL-22 in GVHD target organs contribute to exogenous injected IL-22 as well as secreted IL-22 from the infiltrated allo-reactive effector T cells. In addition, the IL-22R-STAT3 pathway may play important role in GVHD tissue injury and target this way may yield new approaches for reduction of GVHD.