Donepezil hydrochloride (Aricept) has been approved to treat symptoms associated with mild to moderate Alzheimer's disease (AD). Aricept has been shown to improve the memory and thinking abilities, activities of daily living and global function in patients. The purpose of the study is to further investigate the effectiveness and safety of donepezil in patients with severe Alzheimer's disease.

Donepezil is thought to work in the brain by increasing the levels of an important brain chemical called acetylcholine. This chemical helps a person's memory to work better.

Inclusion Criteria:

• Clinically diagnosed Alzheimer's Disease with MMSE score 1~12
• Have not been treated by any medication for Alzheimer's Disease in past 3 months
• Live in community or Assisted Living Facility
• Healthy or with chronic diseases that are medically controlled or stabilized
• Able to swallow tablets

Exclusion Criteria:

• Any primary neurological or psychiatric diagnosis (including depressive disorder) other than Alzheimer's Disease
• Dementia caused by organic diseases other than Alzheimer's Disease