Background: Caring for people with dementia (PWD) is stressful and poses many life challenges for the family caregivers. Interventions targeting the stress and psychological well-being of the caregivers have been proposed but the sustainable effects and efficacies of these interventions vary considerably. Mindfulness-based cognitive therapy (MBCT) has been shown to be effective at reducing stress in several populations. However, limited research on the effects of MBCT in family caregivers of PWD has been conducted. This study protocol aims to examine the effects on stress reduction of a modified MBCT for family caregivers of PWD. Methods: A prospective, single-blind, parallel-group, randomized controlled trial will be adopted. A convenience sample of 100 community-dwelling family caregivers of PWD will be randomized to either the modified MBCT or the control groups. The modified MBCT group will receive a 10-week, seven-session, group-based modified MBCT whereas the control group will receive a social interaction and routine education (SIRE) on dementia care program at a frequency and timing similar to those in the intervention group. The primary outcomes (stress) and secondary outcomes (depression, anxiety, burden, health-related quality of life, and the behavioral and psychological symptoms of the care recipient) will be measured immediately post-intervention (T1) and at 6-month follow-up (T2), which will be compared with the baseline (T0). Discussion: Reducing the stress of caregiving can promote the well-being of the family caregivers and maintain their sustainability in providing daily care for their family members with dementia. MBCT is found to be effective for stress reduction in other populations, and the results of this study are able to provide us with evidence for using MBCT as a standard supportive intervention for the family caregivers of PWD. Trial registration: ClinicalTrials.gov, NCT03354819. Registered on 28 November 2017.