The purpose of this study is to investigate the impact of some corporate governance mechanisms on information asymmetry. From among different mechanisms of corporate governance, the number of board members who were not responsible, ownership concentration and the percentage of institutional ownership are considered. Time scale of the study includes the years from 2005 to 2011. Sampling was performed among all the companies accepted in Tehran Stock Exchange using systematic removal method. This sample includes 504 companies-years. This is a post-event study. Experimentally, this study lies in accounting proving research areas and it is based on financial statements of the firms, and regarding purpose is application. Descriptive method has been used in this study. The findings show that there was a positive and significant relationship between the number of board members who are not responsible and the percentage of institutional ownership from the one side, and information asymmetry from the other. In addition, the findings show a negative significant relationship between ownership concentration and information asymmetry.

Auditor independence is associated with the independence of the internal/external auditor from various parties who may have some financial interest in the business being audited. Many countries have set up different rules forcing firms to change their auditors every few years. This helps business retain healthy business. This paper presents an empirical investigation to study the effect of change in auditing system on 90 selected firms from Tehran Stock Exchange over the period 2007-2011. Using a regression model developed earlier by Demerjian et al. (2012a) [Demerjian, P. R., Lev, B., Lewis, M. F., & McVay, S. E. (2012a). Managerial ability and earnings quality. The Accounting Review, 88(2), 463-498.], the study determines a positive impact of change in auditor system on business development.