In case of public limited companies, there has been a separation of ownership from management. There is a lack of congruence between the interests of shareholders and managers. Shareholders always believe in maximizing their wealth while managers may invest the funds provided by shareholders in projects which may increase the size of the company but may provide inadequate returns to the shareholders. Managers are better informed than shareholders about the prospects of the company. Thus, there is an information asymmetry between shareholders and managers. This leads to agency cost. The system should be designed in such a way that it reduces the information asymmetry between them. One of the means in which information asymmetry can be reduced between shareholders and managers is to impose an effective regulation on the companies such that the shareholders are better informed about the prospects of the company. Mandatory disclosures on corporate governance means equity investors in a company have access to more information about the current performance and future prospects of the company. This information effect of corporate disclosures provides better estimates to the investors regarding the expected future cash flows. The reduction in the degree of uncertainty regarding the estimates of the firm�s future cash flows lowers beta (market risk) of the firm. Thus, from a theoretical point of view, the impact of corporate governance regulation has an inverse impact on market risk To achieve the same objective, SEBI, a regulator of the Indian capital market, imposed a regulation for the listed public limited companies with effect from March 31, 2001. This paper attempts to analyse whether the corporate governance regulation has reduced the market risk of the Indian A-Group companies of BSE. To investigate the impact of the regulation on market risk, a sample carrying more than thirteen years time period from March 1995 to August 2008, has been chosen. The results show that neither the corporate governance regulation imposed on March 31, 2001 nor the amendments on the same brought on January 1, 2006 has been able to significantly reduce the market risk of A-Group companies of BSE. However, the investors consider the information content provided in the amendments more genuine and simpler than the information content provided in the original regulation.