Objective To study the expression and regulation of polycystic ovary syndrome (PCOS) susceptibility gene Hmga2 in endometrial receptivity and decidualization. Methods Experiments including early pregnancy, delayed implantation and activation, artificial decidualization and ovarian steroid hormone treatment were performed, and Q-PCR and Western blot analyses were applied to explain the role of Hmga2 in endometrial receptivity.Results The Hmga2 expression increased gradually with pregnancy. Its expression at the implantation site was significantly higher than that at the inter-implantation site,in the embryo activation group than in delayed implantation group, and in the artificial decidualization than the non-decidualization. The expression of Hmga2 was positively correlated with the expression of estrogen and progesterone, and was positively regulated by estrogen and progesterone in vivo.Conclusions Our findings indicate that the expression of Hmga2 is closely related to the embryo implantation process in early pregnancy in mice, is involved in the process of endometrial decidualization, and is influenced by the activated blastocyst and steroid hormones.