Abstract: The Cause of recurrent spontaneous abortion (RSA) is complicated, and almost 50% of RSA unexplained. The imbalance between T helper cell type 1 (Th1) and type 2 (Th2) is the key character of the RSA. Estrogen and its receptor may affect the function of T cell through the way of gene and the fast signal reaction path, then affect the dynamic balance of Thl/Th2 cell factor，eventually cause the RSA. The low expression of estrogen acceptor in the villi and decidual tissues may cause the RSA. We analyse the function of estrogen receptor and T cell, especially focused on the estrogen receptor to find the cause of RSA.

Key words: Recurrent spontaneous abortion, Estrogen, Estrogen receptor, Tlymphocytes