Estrogen is of great importance in regulating normal reproductive and non-reproductive functions. Aromatase is a key enzyme for the biosynthesis of estrogen in the body. The physiological roles of estrogen is mediated by estrogen receptors (ERs). When estrogen levels and/or the expression of its receptor protein are disrupted in the body, it can lead to diseases such as osteoporosis, and may increase susceptibility to diseases such as alzheimer's disease (AD). This paper reviews the relationship between estrogen and AD susceptibility.