Objective:to study cognitive impairment and social function of patients with Alzheimer disease (AD). Method:22 patients with AD and 12 with depression in elderly were followed for 3 months, both at the very beginning and the end of 3 months, they were tested with CASI (cognitive abilities screening instrument) and FAQ (functional activities questionnaire).Result:scores of short memory, attention, mathematics, abstract and association of CASI were significantly lower in AD group than that in depression group. AD patients had also poorer outcome in FAQ, such as in that of shopping, learn new things, and recall of engagement.Conclusion:Cognitive impairment and social function of patients with AD were poorer than elderly patients with depression.