The present study was designed to investigate the effects of mifepristone on apoptosis of the decidual tissue cells and apoptotic correlated gene Fas/FasL expression in human early gestational period. The extent of DNA fragmentation of apoptotic cells were assessed by using an in situ terminal transferase reaction to label free 3′ ends of the DNA.The expression of Fas, FasL in the deciduas was examined by in situ hybridization with cDNA probe and immunohistochemical staining with polyclonal antibodies, respectively. The results showed that there were evident apoptosis in decidual tissues at about 40 days of gestation. Fas and FasL were strongly expressed in these decidual tissues. At about 50 days of gestation, there were a few apoptotic cells in the decidual tissues. Expression of Fas, FasL decreased at the same time. More apoptotic cells were observed in decidual tissues after adiministration of Mifepristone (RU486) in about 50 days of gestation. Fas, FasL mRNA and protein were up regulated after administration of Mifepristone. The results suggested that the induction of apoptosis by Mifepristone in decidual tissues might be one of the major mechanisms with regards to contraceptive and antigestational effects of mifepristone. Fas pathway might participate in the process of decidua apoptosis induced by RU486.