BACKGROUND In many humanized mouse models, there are few T cells in the engrafted human cell, whereas the number of B cells is high. We attempted to overcome this limitation and investigate whether the entire process of human T cell development arose similarly to the process in humans, as previously reported. METHODS To produce an advanced humanized mice model, we transplanted human fetal liver/thymus tissue subrenally and injected human CD34(+) stem cells intravenously into NOD/SCID/IL2Rgamma null (NSG) mice. RESULTS Humanized mice transplanted with fetal thymus/liver tissues and fetal liver-derived CD34(+) stem cells (FLT+FLCD34) showed higher levels of human cells and T cells than mice transplanted with fetal liver-derived CD34(+) stem cells only (FLCD34). In the transplanted thymus tissue of FLT+FLCD34 mice, thymus seeding progenitors (TSPs), early thymic progenitors (ETPs), pre-T cells, and all the other human T cell populations were identified. In the periphery, FLT+FLCD34 mice have high levels of CD45RA(+) T cells; conversely, FLCD34 mice have higher levels of CD45RO(+) T cells. The CD45RO(+) T cells of FLCD34 mice proliferated rapidly after stimulation and exhibited innate T cells properties, expressing PLZF (promyelocytic leukemia zinc finger protein). CONCLUSIONS Human T cells educated by mouse MHC II in mice without a human thymus differ from normal human T cells. On the basis of these findings, numerous T cell-tropic human diseases could be explored in our humanized mice and molecular aspects of human T cell development could be also studied extensively.