Leukemia inhibitory factor (LIF), mainly secrected by endometrium gland during peri-implantation, is a glycoprotein with pleiotrophic activity on a wide variety of cell types. The principal function of LIF in vivo may be to regulate the growth and to initiate implantation of blastocyst. LIF expression is under maternal control, which is influenced by steroid hormones and cytokines. Gp130, a signal transducer receptor component shared by the cytokines such as LIF, IL-6, OSM and CNTF,can convert the low affinity LIFRβ into a high affinity form, and its homodimerization (in the case of IL-6) or heterodimerization (in the case of LIF,OSM and CNTF) can activate tyrosine kinases, which further regulate expression of target genes by some kinds of pathway.