This study examines the effects of a significant reform to South Korea's social pension system-the introduction of the Basic Pension (BP) in July 2014-on suicidal behavior among older adults. We utilized data from the Korean Welfare Panel Study (2011-2021) to evaluate whether this reform has helped reduce suicidal behavior among BP beneficiaries compared to non-beneficiaries. Employing the Callaway and Sant'Anna Difference-in-Differences (CSDID) approach for a robust analysis, our findings report a significant reduction in suicidal behavior, particularly among women, with an overall reduction of 1.3%. The study highlights the policy effect of the BP in enhancing the economic and mental health stability of older adults, demonstrating the effectiveness of a generous old-age income security program in mitigating factors that contribute to high suicide mortality. These insights are crucial for policymakers aiming to strengthen the welfare state and improve public health outcomes in similar contexts globally.