This project studies the labor supply and income growth effects of the National Basic Livelihood Security System reform in South Korea. In 2015, Korean government redesigned the major social security system to alleviate the problem of potential dependence on welfare and limited coverage by diversifying the type of allowance (from the integrate allowance to the customized allowances) and selection criteria. Using Korean Welfare Panel Survey for 2010-2016, I investigate the impact of the reform on labor supply and income growth by employing difference-in-differences estimation. The evidence suggests that the reform has significantly decreased labor supply by 6.9 percentage points, for the old group aged 41-65, whereas the result is not significant for the young group aged 19-40. However, the reform positively affects the income growth of the low-income individuals, although the result is significant only for the younger group. This finding provides an important policy implication for the direction of effective social security reform, which needs to be customized further to reflect heterogeneous characteristics of the potential and incumbent beneficiaries and facilitate work incentives based on such consideration.