To the best of our knowledge, this is the first study to explore the influence of corporate governance and global financial crisis on firms’ leverage ratio in Taiwanese stock market. The results show the significant impact of the board size on firms’ leverage. Nevertheless, before the global financial crisis, the board size does not have a significant negative impact on firms’ leverage. More importantly, the board size has a significant negative impact on firms’ leverage during and after the crisis. Moreover, the impact is on short-term firms’ leverage. Furthermore, the board size has a stronger negative effect on short-term firms’ leverage during and after the crisis than before the crisis. These findings have investment and management implications for Taiwanese investors, financial institutions and the authorities.