Background: Alzheimer's disease is a progressive neurodegenerative disease. Although some of the current treatments offer some symptomatic relief, this disease cannot be cured at present. Electroacupuncture may be effective for Alzheimer's disease for cognitive function, but the evidence for its effectiveness is still limited. The aim of this study is to evaluate the add-on effect of electroacupuncture to donepezil for improving the cognitive function of Alzheimer's disease. Methods/design: A total of 334 participants with Alzheimer's disease will be randomly assigned to either an electroacupuncture combined with donepezil group or a donepezil group with a ratio of 1:1. Participants in the electroacupuncture combined with donepezil group will receive electroacupuncture in addition to donepezil for 12 weeks and will keep taking donepezil for the following 24 weeks. Participants in the control group will take donepezil only. The primary outcome is the change from baseline in the total score of the Alzheimer's Disease Assessment Scale-cognition at week 12. A follow-up will be conducted 24 weeks after the treatment. Discussion: We expect to verify the hypothesis that acupuncture in addition to donepezil is better than donepezil in improving the cognitive function of patients with Alzheimer's disease. This trial has a limitation that participant blinding is impossible.