Objective Given the high suicide risk among people with schizophrenia and other mental disorders and the significance of intervention in the daily life setting, tailored gatekeeper training is necessary for families of people with mental disorders. This study evaluated the effectiveness of a suicide prevention education program for families of people with mental disorders (SPEM-F), developed by the Korea Foundation for Suicide Prevention.Methods Fifty-nine family members of people with mental disorders were recruited from eight community psychiatric rehabilitation centers in Korea and enrolled in a cluster randomized controlled trial. Four facilities were randomized to the experimental group (n=30) and four to the control group (n=29). The study parameters were measured at baseline, post-intervention, and 1-month follow-up; the effects of SPEM-F (90 minutes, conducted offline) were analyzed using repeated-measures analysis of variance. The dependent variables were suicide-related knowledge, attitude, self-efficacy, preventive behavioral intention, and family problem-solving communication.Results The experimental group showed significant increases in suicide-related knowledge (p<0.001), self-efficacy (p<0.05), and preventive behavioral intention (p<0.01) compared with the control group until the 1-month follow-up, including an upward trend in improved family problem-solving communication (p=0.069).Conclusion The results confirm that SPEM-F is an effective evidence-based gatekeeper training program for families of people with mental disorders, as it focuses on knowledge, self-efficacy, preventive behavioral intention, and communication improvement. As families of people with mental disorders including schizophrenia, are both highly motivated and close to people at high risk for suicide, SPEM-F can effectively promote suicide prevention and gatekeeper activities.