This paper investigates the effect of green bond certification on bond yields. Using a multiple linear regression model estimated via Ordinary Least Squares (OLS), the analysis is based on a sample of 238 bonds issued between 2015 and 2025. We find a positive relationship between certified green bonds and yield, implying that certified green bonds have yields 0.707 percentage points higher than self-labeled green bonds. Moreover, we incorporate interaction terms to examine how certification interacts with the issuer’s credit risk, Environmental, Social, and Governance (ESG) scores, and bond maturity. We find that certified green bonds with longer maturities exhibit a statistically significant negative relationship. In contrast, ESG scores and issuer credit risk do not moderate the relationship between certification and yield. Based on these findings, we recommend the development of a globally standardized definition and certification process for green bonds to enhance market transparency, credibility, and comparability.