Endometriosis, a common estrogen-dependent condition affecting 8-10% of women of reproductive age, is characterized by the presence of ectopic endometrial tissue outside the uterus, leading to pain, morbidity, and infertility. The precise cause of endometriosis remains unclear, and its associated infertility mechanisms are not well understood. Natural killer (NK) cells, crucial for successful pregnancy, have been investigated for their potential role in endometriosis. Research suggests that NK cells play multifaceted roles in regulating endometrial stromal cells (ESCs), promoting immune tolerance, influencing endometrial receptivity, oocyte development, and embryo implantation, thereby contributing to infertility and miscarriage in endometriosis patients. This review aims to summarize current literature and provide an overview of the implications of NK cells in endometriosis, particularly concerning infertility and pregnancy loss, under the influence of estrogen. The review covers the periodic changes in NK cells during the menstrual cycle, the proportion, phenotype, and function of NK cells in normal endometrium and endometriosis, the regulation of estrogen on the differentiation of endometrial NK cells, and the estrogen-NK cell axis in endometriosis. It also discusses the role of the estrogen-NK cell axis in endometriosis-related infertility and miscarriage, including abnormal ovarian follicular development, embryotoxicity of peritoneal fluid, implantation failure, and pregnancy loss. The review highlights the complex interactions between NK cells and endometrial cells, emphasizing the need for further research to fully understand these interactions and their implications in endometriosis. The findings suggest that modulating the estrogen-NK cell axis may represent a potential therapeutic approach for addressing endometriosis and related infertility.Endometriosis, a common estrogen-dependent condition affecting 8-10% of women of reproductive age, is characterized by the presence of ectopic endometrial tissue outside the uterus, leading to pain, morbidity, and infertility. The precise cause of endometriosis remains unclear, and its associated infertility mechanisms are not well understood. Natural killer (NK) cells, crucial for successful pregnancy, have been investigated for their potential role in endometriosis. Research suggests that NK cells play multifaceted roles in regulating endometrial stromal cells (ESCs), promoting immune tolerance, influencing endometrial receptivity, oocyte development, and embryo implantation, thereby contributing to infertility and miscarriage in endometriosis patients. This review aims to summarize current literature and provide an overview of the implications of NK cells in endometriosis, particularly concerning infertility and pregnancy loss, under the influence of estrogen. The review covers the periodic changes in NK cells during the menstrual cycle, the proportion, phenotype, and function of NK cells in normal endometrium and endometriosis, the regulation of estrogen on the differentiation of endometrial NK cells, and the estrogen-NK cell axis in endometriosis. It also discusses the role of the estrogen-NK cell axis in endometriosis-related infertility and miscarriage, including abnormal ovarian follicular development, embryotoxicity of peritoneal fluid, implantation failure, and pregnancy loss. The review highlights the complex interactions between NK cells and endometrial cells, emphasizing the need for further research to fully understand these interactions and their implications in endometriosis. The findings suggest that modulating the estrogen-NK cell axis may represent a potential therapeutic approach for addressing endometriosis and related infertility.