Corporate Governance has gained greater importance to companies and research worldwide. Through this concept, corporations are understood as governance structures in which relationships become important due to the separation of control and management. In Brazil, with the changes occurring since the early 90s related to increasing foreign trade, privatization and monetary stabilization, new players appeared in the national context, raising new corporate governance models. Changes have been observed in the ownership control of corporations nationwide, making institutional and foreign investors principal stockholders. This study seeks to verify if the implementation of good corporate governance passes on measurable benefits to public traded corporations in Brazil. Specifically, does disclosure or the Supervisory Board structure of listed companies in Brazil affect their market value and equity cost of capital? A descriptive, documental and bibliographical research was done aiming to verify the existence of a statistically significant relation between transparency and nondisclosure independent variables and firm value and their equity cost of capital related variables. A multiple linear regression model was applied to a sample of listed companies in Brazil in 2004 with 95% of statistic confidence level. Although without conclusive results, the analysis is linked to the existing codes of conduct related to corporate governance in Brazil.