Objective To investigate the expression of cytokine leukemia inhibitory factor(LIF) in the process of embryo implantation in rat uterus. Methods The immunohistochemical ultra sensitive SP method was used to detect the expression of LIF protein in uterus. Results The expression of LIF was observed in uterine luminal epithelial cells,glandular epithelial cells,stromal cells,muscle cells and vascular endothelial cells;furthermore,immunoreactivity was stronger.Conclusion LIF plays important roles in the process of implantation of earlier embryo.