The rising cost of trading disrupts investors' strategies and reduces return on investment. Planning on this issue through strong mechanisms of corporate governance can reduce trading costs. To this end, the present paper examined the effect of some mechanisms of corporate governance on the stock trading cost. The population consisted of 97 firms enlisted on Tehran stock Exchange during 2009-2016. The hypotheses were analyzed using multivariate regression model. The results showed that major firm owners exacerbate information asymmetry among minority shareholders and uninformed investors through access to confidential and internal information, and thus increase the stock trading cost. Moreover, personal incentives of directors such as ownership requires investors to understand, process and interpret information, and to impose the stock trading cost on investors. Other results showed that the quality of information improves and the stock trading cost reduces because of the role of independent members of the board of directors in monitoring activities of directors.