Decisions regarding end-of-life care are often made by surrogate decision makers, such as family members. These decisions can place a significant psychological burden on surrogates, especially when the patients' wishes are unclear. Advance care planning (ACP) is a patient-centered preconsultation process that is expected to improve the mental health of surrogate decision-makers. This study aimed to clarify the impact of ACP intervention on the mental health of bereaved families and verify its effectiveness. This review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. MEDLINE, EMBASE, PsycINFO, and Cochrane Central Register of Controlled Trials were searched for studies evaluating ACP interventions published up to 2024. Studies were independently selected by two researchers using the Covidence systematic review software (Veritas Health Innovation, Melbourne, Australia). The inclusion criteria were (i) studies evaluating the effectiveness of ACP interventions, (ⅱ) studies reporting bereaved mental health outcomes, and (ⅲ) randomized controlled trials (RCTs). Among the 2,025 studies initially identified, 12 RCTs were included. All interventions involved health professionals trained to facilitate ACP discussions before the patient died. Mental health was assessed using depression, anxiety, and posttraumatic stress disorder scales. The items for which significant differences were reported varied among the studies, but several studies reported effectiveness in treating depression in bereaved families. Furthermore, when baseline-adjusted results were included, ACP interventions reduced post-bereavement anxiety and stress experienced by families. In conclusion, depending on the targets and intervention methods, pre-death discussions may improve the mental health of bereaved families. Thus, ACP should be implemented to help bereaved families.