Objective:to study cognitive impairment of patients with Alzheimer disease (AD). Method:62 patients with AD and 159 normal elderly were tested with MMSE. Result:The patients group had lower scores in all subtests except that of naming. Level of education had positive correlation with the total score, subscores of attention and calculation, understanding, and describe graph. Conclusion:MMSE can be used in clinical assessment of cognitive function of patients with AD.