Purpose : This study aimed to systematically review the effectiveness and characteristics of chatbot-based mental health interventions, with a specific focus on depression and suicide prevention. Methods : A systematic review was conducted following the PRISMA guidelines. Randomized controlled trials (RCTs) published between January 2015 and May 2025 were searched for across five databases: PubMed, CINAHL, Web of Science, RISS, and KISS. Eligible studies involved chatbot-based interventions targeting depression, suicide-related outcomes, or other mental health symptoms. Key characteristics, intervention content, target populations, and outcomes were extracted and analyzed. Results : Nine RCTs met the inclusion criteria. Participants included individuals with a high risk of suicide or depression (e.g., those with a major depressive disorder or eating disorder), psychologically vulnerable populations (e.g., those experiencing chronic stress or headaches), healthcare professionals, university students, and the general adult population. The chatbots integrated components such as cognitive behavioral therapy (CBT), mindfulness, psychoeducation, relaxation techniques, motivational interviewing, and emotional support. Across the studies, chatbot interventions demonstrated significant positive effects in reducing depression, anxiety, stress, and somatic symptoms, and in improving self-efficacy, emotional well-being, and behavioral change intentions. However, no RCT directly targeted suicide prevention as a primary outcome, indicating a significant research gap in this area. Conclusion : Chatbot-based interventions offer promising, scalable tools for supporting mental health across diverse populations. They are particularly effective for managing depression and related symptoms through cognitive and emotional mechanisms. Nevertheless, evidence for their use in suicide prevention remains insufficient. Future research should explore chatbot designs specifically aimed at suicide prevention, assessing long-term effects and ensuring ethical and clinical safety in real-world applications.