Abstract:As the only exception to the immunological principles， maternal-fetal tolerance becomes the attention focus in the fields of reproductive immunology. An improved mechanistic understanding of maternal-fetal tolerance is emerging in the last century. The formation of a functional synapse of the invading fetal trophoblsats， decidual immune cells and dicidual stromal cells has now been recognized. Here we review the previous research results， with a special focus on the establishment and maintenance mechanism of maternal-fetal tolerance based on the maternal-fetal crosstalk. Insights into maternal-fetal tolerance will not only improve our understanding of normal pregnancy but also would be helpful to novel therapeutic strategies of the pregnancy miscarriage， pre-eclampsia and IUGR.