Background: Caregivers of people with dementia experience high stress levels. Mindfulness-based cognitive therapy has been found to be effective in reducing stress and improving the psychological well-being of several populations. Objective: To explore the feasibility and preliminary effects of a modified mindfulness-based cognitive therapy for family caregivers of people with dementia. Methods: In a single-blinded, parallel-group, randomized controlled trial, 36 caregivers of people with dementia were randomized to either the intervention group, receiving the 7-session modified mindfulness-based cognitive therapy in 10 weeks; or the control group, receiving the usual family care and brief education on dementia care. The brief education sessions were similar in frequency and duration to the intervention group. Various psychological outcomes of caregivers were assessed and compared at baseline, immediately post-intervention, and at the 3-month follow-up. A focus group with eight participants from the intervention group was conducted to identify the strengths, limitations, and difficulties of the intervention. Results: Intervention feasibility was established with a high completion rate of 83% (completing ≥5 out of the 7 sessions) and a low attrition rate of 11.1%. The duration of the average weekly home-based mindfulness practice of the caregivers was 180 minutes (S.D. = 283.8). The intervention group experienced a statistically significant decrease in stress levels (Z = -1.98, p = 0.05, Cohen's d = 0.7) and depressive symptoms (Z = -2.25, p = 0.02, Cohen's d = 0.8) at the post-test; and a decrease in stress (Z = -2.58, p = 0.01, Cohen's d = 0.9), depressive symptoms (Z = -2.20, p = 0.03, Cohen's d = 0.7), and burden (Z = - 2.74, p = 0.006, Cohen's d = 1.0), and improved quality of life (physical) (Z = -1.68, p = 0.09, Cohen's d = 0.6) at the 3-month follow-up compared to the controls. A focus group conducted immediately after the intervention revealed three major themes: Impacts on the family caregivers, Impacts on the people with dementia, and Difficulty in practicing mindfulness. Conclusion: The findings support the feasibility and preliminary effects of the modified mindfulness-based cognitive therapy on reducing the stress of caregivers and improving their psychological well-being. Some potential effects on people with dementia (e.g., improvements in behavioral problems) were reported by the caregivers. A future study with a larger and more diverse sample is proposed to evaluate the longer-term effects and generalizability of the modified mindfulness-based cognitive therapy and the impacts on people with dementia.