Family caregivers of patients with chronic mental disorders who are responsible for taking care of the patient face many problems that can endanger the psychosocial health of these people. This study was conducted to develop, implement, and evaluate a psychosocial health promotion program for family caregivers of patients with chronic mental disorders. This research is an exploratory sequential mixed-method study conducted using a qualitative-quantitative design. A qualitative study was conducted to explain the needs and psychosocial problems and the solution to improve the psychosocial health of family caregivers of patients with chronic mental disorders in two psychiatric care centers in Isfahan were conducted. Then the program was written based on Kern's programming development approach. In the quantitative stage, a part of the developed program was implemented as virtual group psychoeducation for 67 caregivers, and its impact on caregivers' burden of care was evaluated. The findings from the qualitative phase of the study led to the emergence of 3 main categories and the findings from the quantitative phase of the study indicated that the implementation of the compiled program causes a significant reduction in the burden of care in family caregivers of chronically mentally ill patients (p<0.05). The current program was prepared and developed using an evidence-based approach. Policymakers and members of the mental health team can take a valuable step toward reducing the care burden of family caregivers of chronic mental patients by using the content of the developed mental health promotion program.