This study will evaluate the pharmacological efficacy on language capability and compliance with combination of new Ebixa oral pump and donepezil compared to donepezil only in patients with probable Alzheimer's disease. Primary objective is to evaluate the efficacy of memantine on language capability in moderate to severe Alzheimer's disease patients who are taking stable donepezil treatment.Secondary objectives are to evaluate the efficacy of maintain on cognitive function and disease progression with K-MMSE, NPI, ROSA, and SIB-short form in probable AD.

Inclusion Criteria:

• probable Alzheimer's disease in accordance with NINCDS-ADRDA criteria
• MMSE score equal to or less than 20
• Brain CT or MRI scan performed within the past 12 months
• living or having regular visit at least three times a week from caregiver
• able to visit outpatient clinic and to perform cognitive function test
• already taking stable dose of donepezil for 3 months prior to screening
• subject and caregiver who signed informed consent

Exclusion Criteria:

• involved in another clinical trial within 4 weeks prior to screening
• severe or unstable disease: acute or severe asthma, unstable or severe cardiovascular disease, acute peptic ulcer,chronic renal failure
• bradycardia (pulse rate less than 50bpm), sick sinus syndrome
• any laboratory finding including cognitive impairments(vitamine B12 or folic acid, syphilis, thyroid disease)
• severe auditory or visual disturbance
• other degenerative disease or psychosis
• taken any drug used for the treatment of Alzheimer's disease or dementia