By exploiting variations in pro-natalist cash grant amounts across 225 municipal districtsin South Korea from 2005 to 2010, we estimated the causal impact of cash grants onfertility. After controlling for administrative district fixed effects, a system GMM analysisrevealed a rise in grant amounts by 1,000 USD increased the crude birth rate by 4.4%. Theresults imply that the required grant amount for one extra birth increases with the parity ofbirths. The sub-group analysis by maternal age suggests that the grant may have asignificant permanent impact on the completed lifetime fertility.