This study aims to examine whether implemented in corporate governance affect firm’s credit rating . With a sample of 168 firms listed in Indonesia Stock Exchange (IDX) during 2009-2013, this study finds that implemented in corporate governance affect on firm’s credit rating and the components positively affect are board size, institutional ownership, audit committee, and external auditor. While proportion of outside director and size of blockholders negatively affect firm’s credit rating. This study also finds that independent commissioner insignificantly associated with firm’s credit rating. This research found the number of directors have inverted quadratic "U" shape relation with credit ratings with maximum point at 4,589. The higher the number of directors will make the credit rating higher, because the monitoring and decision making will be more effective (indicated by positive number of director’s coefficient). However, when it reaches the optimum point, additional number of directors will cause a decrease in management performance (indicated by negative quadratic directional coefficients) because they will experience coordination problems. These results illustrate that the number of directors who can increase the credit rating of the company is only 4,589 (about 4 or 5 people), if exceeding that amount, will lower the credit rating of the company.