Objective To study the regulation of thymosin on the T-lymphocyte subsets of peripheral blood in immunological liver injury mice.Methods The mouse model of immunological liver injury was induced by BCG vacsine and lipopolysaccharide and the effects of thymosin on T-lymphocyte subsets of peripheral blood in immunological liver injury mice were determined and compared with the normal mice.Results The immunological liver injury mice were immuno-deficient because their CD3~+,CD4~+,CD8~+ and the ratio of CD4~+/CD8~+ were lower than those of normal mice.Thymosin effectively enhanced various immune functions and the defence systems of the host by increasing CD3~+,CD4~+ and the ratio of CD4~+/CD8~+.Conclusion Thymosin effectively improves the immune function of the host by regulating the balance between CD4~+ and CD8~+ cells.