Abstract: Estrogen is one of the gonadal hormones that has multiple beneficial actions in central nervous system and involves in learning and memory. Therefore，it has been hypothesized that the change of estrogen levels in women following menopause is associated with cognitive-related diseases. Now，contradictory results in the studies of menopausal or postmenopausal women have prompted speculation that a critical period exists for hormone treatment to protect against cognitive decline in older women. Consistent with this hypothesis， studies in both women and rodents discussed the effects of estrogen on cognitive function and whether the initiation of hormone treatment is an important factor of preventing or exacerbating cognitive impairment by analyzing the change of brain function when estrogen drops and exogenous estrogen is supplied，which is greatly significant for prevention and treatment of cognitive decline in women following menopause.

Key words: Estrogens, Cognition, Receptors, estrogen, Estrogen replacement therapy, Menopause