Utilizing the removal of the bank lending interest rate floor (IRFD) in China as an exogenous shock of banking liberalization, we find that IRFD leads to a significant rise in firms’ cost of equity capital, which is consistent with the prediction from the MM theory. The identified effects are more pronounced among firms with weaker ex-ante corporate governance and more severe ex-ante agency problems. We also find that IRFD witnesses an increase in the amount of acquired bank loans, a decrease in the average interest rate, and an increase in free cash flow. Further evidence also suggests IRFD provokes a drop in firms’ investment quality. Overall, our findings highlight an unexplored role of banking sector deregulation on firms’ cost of equity capital.