Alzheimer's disease (AD) is the most common etiology of dementia, that has not been previously reported in Korea. We have experienced two cases of Alzheimer's disease, one occurred in a 53-year-old man with dementia and the other occurred in a 36-year-old woman with a family history of early onset dementia. A neocortical biopsy was done to rule out the cause of dementia and showed diffusely scattered numerous senile plaques and neurofibrillary tangles in cortex of both cases. Interestingly, GFAP, an immunohistochemical stain showed strong positivity in neuritic plaques and the surrounding fibrillary gathering.