The objective is to demonstrate that donepezil hydrochloride 10 mg/day has superior efficacy compared with placebo in cognitive function in Chinese subjects with severe Alzheimer's Disease.

Inclusion Criteria

• Written informed consent (IC) will be obtained from the subject (if possible) or from the subject's legal guardian or legal representative prior to beginning screening activities.
• Subject age range: male and female subjects 50 to 90 years of age, inclusive
• Diagnosis: diagnostic evidence of probable Alzheimer's Disease (AD) consistent with Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision (DSM-IV-TR) and National Institute of Neurological and Communicative Disorders and Stroke-Alzheimer's Disease and Related Disorders Association (NINCDS-ADRDA) criteria
• MMSE 1 to 12 inclusive, at both Screening and Baseline
• SIB less than or equal to 90 and greater than or equal to 10 at both Screening and Baseline
• Comorbid medical conditions must be clinically stable prior to Baseline, unless otherwise specified.

Exclusion Criteria

• Subjects with a known history of disorders that affect cognition or the ability to assess cognition, but are distinguishable from AD
• Evidence of focal disease to account for dementia on any cranial image MRI or CT.
• Subjects with dementia complicated by other organic disease or AD with delirium according to DSM-IV criteria
• Subjects who cannot swallow or who have difficulty swallowing whole tablets, as tablets should not be broken or crushed
• Illiteracy prior to AD
• Subjects who are unwilling or unable to fulfill the requirements of the study
• Treatment with another cholinesterase inhibitor and/or memantine in the 3 months prior to Screening
• Subjects with a poor response (tolerability) to prior exposure to donepezil