This research investigates the relationship between corporate governance (CG) mechanisms and SSB mechanisms on the firm's performance of Islamic bank affected by the mediating variable of CG disclosure. CG is expected to be relevant to Islamic banks in strengthening the infrastructure of Islamic financial institutions (IFIs). Thought a limited amount of research against on CG and performance of Islamic banks has been carried out, this study tries to explore more on the CG and firm performance, particularly in the context of Islamic banks and CG disclosure as a mediating variable to strengthen this relationship. This paper aims to address CG disclosure as a mediating variable as a gap in this study. The empirical procedures involve panel data analysis is applied from the annual reports of Islamic banks in the Southeast Asian (SEA) and the Gulf Cooperation Council (GCC) regions from 2012 to 2017. Based on the reviews past literature, the result provides evidence that stronger CG strength and Shari'ah supervisory board (SSB) strength have a relationship with a higher level of firm performance of the Islamic bank. This study contributes to the literature regarding how CG disclosure as a mediating variable influences the relationship between CG strength, SSB strength and firm performance of Islamic banks.