To examine the effects of a benefit-finding intervention, the key feature being the use of gain-focused reappraisal strategies to find positive meanings and benefits in caring for someone with dementia. In a cluster-randomized, double-blind, controlled trial conducted in social centers and clinics, 129 caregivers aged 18 + and without cognitive impairment, providing at least 14 care hours per week to a relative with mild-to-moderate Alzheimer disease, and scoring ≥ 3 on the Hamilton Depression Rating Scale were studied. Exclusion criterion was care recipient having parkinsonism or other forms of dementia. The benefit-finding intervention was evaluated against two treatment-as-usuals, namely, simplified psychoeducation (lectures only) and standard psychoeducation. Each intervention lasted 8 weeks, with a 2-hour session per week. Randomization into these conditions was based on center/clinic membership. Primary outcome was depressive symptom. Secondary outcomes were Zarit Burden Interview, role overload, and psychological well-being. Self-efficacy beliefs and positive gains were treated as mediators. Measures were collected at baseline and post-treatment. Regression analyses showed benefit-finding treatment effects on all outcomes when compared with simplified psychoeducation and effects on depressive symptoms and Zarit burden when compared with standard psychoeducation. Effect sizes were medium-to-large for depressive symptoms (d = -0.77 to -0.96) and medium for secondary outcomes (d = |0.42-0.65|). Furthermore, using the bootstrapping method, we found significant mediating effects by self-efficacy in controlling upsetting thoughts and positive gains, with the former being the primary mediator. Finding positive gains reduces depressive symptoms and burden and promotespsychological well-being primarily through enhancing self-efficacy in controlling upsetting thoughts.