Existence of human trophoblast stem (hTS) cells has been suspected but unproved. The isolation of hTS cells is reported in the early stage of chorionic villi by expressions of FGF4, FGFR-2, Oct4, Thy-1, and stage-specific embryonic antigens distributed in different compartments of the cell. hTS cells are able to derive into specific cell phenotypes of the three primitive embryonic layers, produce chimeric reactions in mice, and retain a normal karyotype and telomere length. In hTS cells, Oct4 and fgfr-2 expressions can be knockdown by bFGF. These facts suggest that differentiation of the hTS cells play an important role in implantation and placentation. hTS cells could be apply to human cell differentiation and for gene and cell-based therapies.