The Safe Conversion Loan (Ansim Jeonhwan Daechul), launched in 2015, is a policy financial product that refinances existing variable-rate mortgage loans into long-term fixed-rate loans. Following the launch of this product, despite market changes that would generally increase prepayment rates—such as rising housing prices, declining market interest rates, and decreasing mortgage delinquency rates—an anomaly emerged in which actual prepayment rates declined. This study empirically examines whether there was a structural change in the prepayment behavior of mortgage borrowers by conducting a pool-level empirical analysis of the underlying assets of mortgage-backed securities. Additionally, other economic variables capable of explaining prepayment rates were analyzed together, and variables with high explanatory and predictive power were selected. This study has the following implications. First, the change in prepayment behavior after 2015 is a short-term phenomenon attributable to the launch of the policy financial product, and its influence may diminish over time. Second, the impact of housing price changes on borrowers' prepayment decisions has weakened, which can be interpreted as a reduction in the role of collateral housing factors in prepayment. Third, the implementation and promotion of the Safe Conversion Loan aroused borrower interest in prepayment, consequently increasing prepayment of existing long-term fixed-rate loans as well. However, given the overall environment related to mortgage loans—including the currently low interest rate levels and increasing upward pressure on domestic interest rates due to U.S. benchmark interest rate hikes—its impact may be limited. Fourth, the study confirmed that an indicator utilizing search term frequency analysis related to prepayment has explanatory and predictive power for actual prepayment behavior.