The physiological functions of the ovary and development of the corpus luteum occur through the activation of endocrine hormones. In this process, estrogen, a reproductive hormone, is secreted in the ovarian follicle and corpus luteum and affects corpus luteum formation and regression. Estrogen controls the synthesis of reproductive hormones by binding to estrogen receptor–α and –β. Estradiol–17β, synthesized in the ovary, regulates the physiological function of the corpus luteum and the angiogenesis signaling pathway. Estrogen controls progesterone synthesis, which is regulated by StAR-transported cholesterol, P450scc-converted pregnenolone in mitochondria, and 3β-HSD-synthesized progesterone in the smooth endoplasmic reticulum. Estrogen secretion is also stimulated by kisspeptin and regulated by gonadotropin-releasing hormone, follicle-stimulating hormone, and luteinizing hormone. Moreover, the formation of the corpus luteum is closely regulated by angiogenesis. VEGF is an important factor in angiogenesis and plays a role in the survival, proliferation, and migration of endothelial cells. Especially, VEGF–A is a key factor in the physiological functions of endothelial cells. VEGF binds VEGFR–2 and affects the signaling pathways of PI3K, Akt, MAPK, and ERK. Also, VEGF binds to HIF–1α, inducing VEGF secretion. Estrogen promotes the activation of HIF–1α, while the activation of mTOR and Akt stimulates VEGF secretion. Therefore, estrogen is a major reproductive hormone in physiological function and the synthesis and secretion of endocrine hormones in the ovary and corpus luteum