To study the contribution of T cell subsets in the pathogenesis of Murine hepatitis virus Type3 (MHV-3) induced chronic viral hepatitis in C3H/Hej mice, ninety C3H/Hej mice were chosen to individually receive 10 plaque forming units (PFU) of MHV-3 intraperitoneally. The changes of virus titer and pathology in liver tissue were examined by standard plaque assay and by the hematoxylin/eosin (HE) staining method from 2 days post MHV-3 infection. The ratios of T cell subsets including CD3+CD4+CD8-, CD3+CD4-CD8+, CD3+CD4-CD8-, CD3+CD4+CD25+, CD3+CD4+CD25- and CD3+CD4-CD25+ T lymphocyte of total T lymphocytes in blood, spleen and liver were examined at 0, 2, 4, 6,8, 10, 12, 15, 20, 25, 30, 40 days post MHV-3 infection by flow cytosorting. We observed that the virus titer raised and showed persistent virus duplications and inflammatory changes in the livers of C3H/Hej mice from 2 days post MHV-3 infection. The double negative T cell (DN Treg cell) and CD4+CD25+ T cell ratios increased significantly from 2 days post MHV-3 infection in C3H/Hej mice, and CD3+CD4+CD8-, CD3+CD4-CD8+, CD3+CD4+CD25- and CD3+CD4-CD25+ T cell ratios decreased accordingly. In conclusion, the changes of virus titer and pathology in the livers of C3H/Hej mice post MHV-3 suggest their contribution to viral persistence. Further characterizations of DN Treg cells are that infection indicates that MHV-3 could induce the chronic inflammation in livers of C3H/Hej mice.The increase of the DN Treg cell and CD4+CD25+ T cell ratios in C3H/Hej mice post MHV-3 infection suggests that DN Treg cells and CD4+CD25+ T cells may both have important suppressive immunomodulation functions in the development of chronic viral hepatitis and have important roles in the virus persistent infection. Further characterizations of DNT cell and CD4+CD25+ T cell are under investigation.