Abstract: Objective： To explore the relationship between the saffron and the expression of leukemia inhibitory factor(LIF) in the endometrium of early pregnant mice. Methods: The mated female mice were orally treated with saffron solution in a dose of 10.5g/kg, 15.5g/kg and 20.5g/kg or physiological saline (control)， on the 2nd, 3rd and 4th days after fertilization. The uteri of the mice were removed and routinely sectioned 24 hours later. The morph of the endometrium was observed with HE and the expression of LIF in the endometrium of the mice was analyzed with immunohistochemistry and Quantimet. Results: The endometrium was in congestion and disorder in the experimental groups; with increasing doses of saffron, the endometrium gradually changed. The LIF was expressed strongly in the murine endometrium of control group. The expression level of LIF in experimental groups was much lower than that in the control group（P＜0.05, P＜0.01）and decreased gradually with increasing doses of saffron. Conclusion: Saffron can inhibit the expression of LIF in the endometrium of pregnant mice, and therefore interferes with the implantation of embryos.

Key words: Saffron, LIF protein, Endometrium, Anti-early pregnancy