I investigate the substitutability between social security and private savings via Korean Pension Reform. In 2016, two special occupation pensions changed: civil servant pension and private education school pension. Due to the accumulation of deficits in the two public pensions, the Korean government increased individual contributions and decreased benefits in both social securities. On the other hand, other public pensions remained unchanged. These changes provided a quasi-experimental environment to understand the relationship between social security and private saving. Through the DID method, reductions in public pensions increased private savings by 13-17 percent. And low income or old-aged households show the bigger substitutability between social security and private savings.