Estrogen has its receptor in the brain and affects the nervous system in various ways. To date, it has been paid attention whether the cognitive function and the risk of depression change due to estrogen deficiency and also whether these changes respond to hormone replacement therapy (HRT). The increase in female life expectancy accelerates the prevalence of dementia like Alzheimer Disease, so the efficacy of HRT in the cognitive function got the public attention. On the contrary, a series of large-scale randomized controlled trials (Women's Health Initiative Memory Study: WHIMS) in aged 65 years or older women showed HRT increases the risk of dementia. However, certain studies indicate HRT may have beneficial effect on dementia when being started earlier. Therefore direct application of the result of WHIMS for the climacteric women is still controversial.