When caring for an older relative with dementia, family members experience considerable distress and burden. Literature reviews show that supportive group interventions for these caregivers have significant positive effects on improving their distress and quality of life, but not consistent and conclusive. Limited research is found in Asian populations. This study tested the effectiveness of a 12-session bi-weekly mutual support group program for Chinese family caregivers of a relative with dementia in Hong Kong, when compared with standard family support service. An experimental study with pre- and post-test, parallel groups design was conducted. A randomized sample of 78 family caregivers, 39 in each of the experimental and control groups, from one regional dementia care center participated in the study. A protocol was specifically designed by an advanced practice nurse to guide the mutual support group process and the facilitator and peer leader training, based on evidence from the literature on family support group intervention in Western countries. The results of ANOVA tests indicated that the mutual support group participants had significantly greater improvements in distress levels and quality of life than the control group. There were only mild changes in the demands for mental health services in both groups at post-test. These findings support the effectiveness of mutual support groups to offer psychosocial support to Chinese family caregivers in dementia care beyond routine community mental health care.