ABSTRACT This paper examines the effects of the collateral-based monetary policy, implemented by the People’s Bank of China, on green financing costs. Employing a Difference-in-Differences (DID) method to examine credit spreads of financial bond in primary and secondary markets from 2017 to 2019, our findings highlight a significant decrease of 26 basis points (bps) in the financing costs of green financial bonds in the primary market, with a 12-bps decline in the secondary market post-policy. Our study underscores the crucial role of implicit credit enhancement provided by the People’s Bank of China's collateral endorsement. Interestingly, the liquidity provision mechanism, where investors pay premiums to secure liquidity support, does not find empirical backing in the specific context of China's bond market. These findings illuminate the effectiveness of collateral-based monetary policies in reducing green financing costs, offering valuable insights for using collateral strategies to green monetary policies.