An effective internal control system and the degree of compliance with corporate governance principles are important factors in ensuring the continuity of companies in capital markets. Financial performance is the most commonly used indicator for monitoring continuity. In the literature, there are studies investigating whether the internal control system and corporate governance principles have an effect on financial performance. However, there is no study investigating moderator effect of the internal control system on the financial success of corporate governance. For this purpose, it was examined in this study whether there was a moderator effect of the internal control system on financial success of corporate governance. The study was conducted on companies in the Borsa Istanbul (BIST) corporate governance index (XKURY). The effectiveness of the internal control system was determined by the survey method, and then corporate governance effectiveness ranking was created with corporate governance rating scores. The moderator effect was investigated by regression analysis using the data obtained. As a result of the analysis, it has been determined that the internal control system has a moderator effect on the financial success of corporate governance. On the other hand, it is concluded that although corporate governance is thought to have a moderator effect on the financial performance of the internal control system, it does not. The reasons for this theoretically unexpected result were investigated in the study.