The aim of this study was to evaluate the effect of thrombopoietin (TPO) on T lymphocyte in Balb/c mice delivered hTPO cDNA with plasmid vector. Both mature and immature T lymphocytes in central organs increased, but only the CD4+ subset was preferably proliferated in circulation. High serum IFN-gamma was coinciding with the declination of platelet counts, but TNF-alpha was positively associated with the platelet count, while high IL-2 level was similar to the course of TPO expression. Our data suggested that TPO is a stimulator for T lymphocytes, especially the CD4+ subset.