This research aims to explore the Moderating Effect of Corporate Governance (CG) Gender Diversity on the relationship of CG attributes and Financial Performance of Listed Companies in Sri Lanka, The sample of the study consists of all companies listed in CSE exclusive of bank & financial institutions which are practicing unique governance practices issued by CBSL. The final sample consists of 183 listed non-financial companies during the period of 2009 to 2015. This research deployed panel data regression analysis to test the relationship formulated in the hypotheses by using the E view 9 software. The results showed that the board structure related variables such as separate leadership structure, proportion of nonexecutive director on board, and women representation on boards appeared to be significant influence on agency costs. Meanwhile, board size and presence of interlocking directorship on boards does not have any direct impact on agency costs. On the other hand, all selected board structure variables did not have any direct impact on shareholder wealth of companies listed in Sri Lanka. The findings of this study regarding board structure, agency costs and shareholder wealth have important managerial implications that these findings are unlikely to the prediction of theory and best practices. Agency theory is not applicable of these companies since the exiting corporate governance practices increase agency costs. The potential benefits of this study led to rethink the board of directors of the companies,managers, shareholder, and the policy makers to re organize the implementation of best practices.