The main purpose of this study is to investigate the relationship between Corporate Social Responsibility and costs of debt. Besides, this study also examines the moderating effect of Credit Rating Index on the relationship between Corporate Social Responsibility and costs of debt. Corporate Social Responsibility index came from Market Observation Post System. The sample used in this study includes all, except financial-related firms, the listed company in Taiwan between 2012 and 2013. The empirical results show that the firms with more CSR have better costs of debt. Furthermore, this research also find that credit rating Index play a significant moderating role in the relationship between corporate social responsibility and costs of debt.