Objective To investigate the expression of mixed lineage kinase domain-like protein (MLKL) in uterus during early pregnancy and decidua in mice. Methods Different mouse models including early pregnancy model, artificially induced decidualization model and hormone and/or progesterone treatment of uterine model were constructed; human endometrial stromal cells were cultured in vitro and were induced for decidualization by treating with estradiol-17β, medroxyprogesterone acetate and dibutyryl cyclic adenosine monophosphate. The expression of MLKL mRNA and protein in the uterus of early pregnancy, decidual uterus, and hormone-treated uterus in mice were analyzed by real-time fluorescent quantitative PCR, in situ hybridization and Western blotting. The expression of MLKL mRNA in human decidual cells induced in vitro was detected by real-time fluorescent quantitative PCR. Results (1) In the uterus during early pregnancy in mice, the expression of MLKL mRNA and protein in uterine epithelium on the 1^st to 4^th day of pregnancy (day 1 was day of vaginal sperm) was low and irregular. It was expressed in the uterine epithelium and surrounding decidual cells on the 5^th day of pregnacy, and was mainly expressed in the decidua from the 6^th to 8^th day of pregnancy. After the implantation, the expression of MLKL mRNA and protein was day-by-day increased and reached the highest on the 7^th day of pregnancy, with a slight decrease on the 8^th day. (2) In the uterus of mice with artificially induced decidualization, MLKL mRNA was expressed in the entire decidual region with high level; while there was no significant expression in the uterus of the control mice. The expression of MLKL protein was consistent with the expression of MLKL mRNA. The expression of MLKL mRNA in human decidual cells induced in vitro was significantly higher than that in the control group (P<0.05). (3) The expression of MLKL mRNA and protein in progesterone-treated uterus was significantly increased compared with the control group (P<0.05). Conclusion MLKL regulated by steroid hormone progesterone is involved in embryo implantation and decidualization of mammals.