BACKGROUND: Caregiver stress can pose serious health and psychological concerns, highlighting the importance of timely interventions for family caregivers of people with dementia. Single-session mindfulness-based interventions could be a promising yet under-researched approach to enhancing their mental well-being within their unpredictable, time-constrained contexts. This trial will evaluate the effectiveness and feasibility of a blended mindfulness-based intervention consisting of a single session and app-based follow-up in reducing caregiver stress. METHODS/DESIGN: The study is a single-blinded randomized controlled trial with two arms (intervention versus an education session on dementia care) and assessments at baseline, 8 weeks, and 6 months. The eligibility criteria include: family caregivers aged 18 years or older; providing care for an individual with a confirmed medical diagnosis of dementia for at least 3 months prior to recruitment, with a minimum of 4 hours of daily contact; and exhibiting a high level of caregiver stress. The intervention comprises a 90-minute group-based session with various mindfulness practices and psychoeducation. Participants will receive a self-practice toolkit to guide their practice over a duration of 8 weeks. Sharing activities will be implemented through an online social media platform. The primary outcome is perceived caregiving stress. The secondary outcomes include depressive symptoms, positive aspects of caregiving, dyadic relationship, trait mindfulness, and neuropsychiatric symptoms of care recipients. The feasibility outcomes include eligibility and enrollment, attendance, adherence to self-practice, and retention, assessed using mixed methods. DISCUSSION: The study will contribute to the evidence base by investigating whether a single-session mindfulness intervention is effective and feasible for reducing caregiver stress among family caregivers of people with dementia. TRIAL REGISTRATION: ClinicalTrials.gov, NCT06346223. Registered on April 3, 2024.