The primary objective of the study is to evaluate the efficacy of T-817MA in AD patients to treat dementia. Efficacy will be cognitive function, as measured by the ADAS-cog cognitive assessment.

The secondary objectives of the study are to evaluate the safety of T-817MA and the activities of daily living (assessed with the ADCS-ADL) of AD patients taking T-817MA, and to evaluate the efficacy of T-817MA in AD patients with an overall global assessment using the ADCS-CGIC.

• Drug: T-817MA
• Drug: Placebo

• Experimental: T-817MA once daily
• Placebo Comparator: Placebo once daily

Inclusion Criteria:

1. Male or female (post-menopausal or surgically sterile)
2. Patients with Mild to moderate Alzheimer's disease who are receiving Donepezil.
3. Age 50 to 90 inclusive
4. Patients must be living in the community
5. Patients must have an eligible informant or study partner (caregiver)
6. Patients and eligible informant or study partner (caregiver) must be able to read and understand English.
7. Informed consent obtained from both the patient and the caregiver etc (According to the protocol)

Exclusion Criteria:

1. Patients with clinically significant cardiac, hepatic or renal impairment
2. Patient have a dementia not of the Alzheimer's type etc (According to the protocol)
3. Patients who are taking any drug other than donepezil for Alzheimer's disease, including rivastigmine (Exelon®), galantamine (Razadyne®), memantine (Namenda™) or tacrine (Cognex®) taken within twelve (12) weeks of the Baseline Visit (Visit 2).