Background <p>Mild cognitive impairment (MCI) is an intermediate stage between normal cognitive aging and dementia. People with MCI have a higher risk of developing dementia than normal healthy people. Improving their cognitive functions may delay dementia onset. The aim of this project is to conduct a randomized controlled trial to assess the effects of transcranial direct current stimulation (tDCS) on cognition in adults with mild cognitive impairment.</p> Methods/design <p>Forty-eight MCI participants will be recruited from four local day centers for the elderly and assigned to experimental or control groups randomly in a 1:1 ratio. Participants and assessors are blinded to their group assignment. The experiment will consist of pre- and post-assessments and a 1-month follow-up assessment. Participants will receive 8 sessions (2×/week for 4 weeks) of tDCS intervention (either real or sham, 20 min per session). Primary outcome measures will include digit span test, color trail test, verbal fluency, Chinese version of the Verbal Learning Test, and the Hong Kong version of Montreal Cognitive Assessment. Participants will also have their brain waves recorded while completing a computer memory task at each assessment point. The task will require them to study and memorize certain Chinese characters and take a recognition memory test. Secondary outcomes include scores from the Geriatric Depression Scale and the Modified Barthel Index.</p> Discussion <p>The study addresses the shortcomings in previous studies and investigates multiple domains of cognition (e.g., attention, memory, executive function), the sustainability of the effects, and includes electroencephalography as an outcome measure with application to people with MCI. The results of this proposed project are expected to have an impact on the long-term care and rehabilitation of older and clinical populations and to increase general knowledge about tDCS and related cognitive enhancement in MCI.</p> Trial registration <p>ClinicalTrials.gov NCT05584748 (<a href="https://clinicaltrials.gov/study/NCT05584748">https://clinicaltrials.gov/study/NCT05584748</a>). Registered on October 10, 2022.</p>