Safety, Efficacy and Dose Titration of Sodium Oligo-mannurarate Capsule on Mild to Moderate Alzheimer's Disease

Inclusion Criteria: * At least primarily educated. * Accord with Probable Alzheimer disease of National Institute of Neurological and Communicative Disorders and Stroke and the Alzheimer's Disease and Related Disorders Association(NINCDS-ADRDA)'s Criteria. * 10 points ≤ Minimum Mean-Square Error(MMSE) ≤ 24 points. * Hachinski ischemia scale \<4 points. * Hamilton depression scale ≤10 points. * Should have stable accompanying person, or at least contact 2 hours per day, 4 days per week with accompanying person. The accompanying person should help the patient throughout the trial. * Signed the information consent form. Exclusion Criteria: * Have been in other clinical trials within 30 days before this trial' start. * women during pregnancy or lactation. * Dementia caused by other diseases. * previous nervous system diseases. * Abnormal laboratory results. * Uncontrolled hypertension. * Unstable or serious diseases of heart, lung, liver, kidney and blood. * Visual or auditory handicap. * Significant focal lesions revealed by electronic computer X-ray tomography(CT) or magnetic resonance imaging(MRI) in one year before enrollment. * Alcohol abuse or drug abuse. * psychotic, including patients with serious depression. * Patients being in drug therapy of Alzheimer disease which cannot be stopped. * In treatment of heparin, Polysaccharide sulfate, mannose ester 3 weeks before the recruitment. * Investigator consider the patient cannot finish this trial for any reason. * Relatives or employees of the investigators, staff of the investigate centers, contract research organization and sponsor.