Realizing the goals of corporate governance requires an efficient and effective board, so achieving this goal requires an assessment of the board's characteristics. Therefore, it is expected that the board, which is the most important and cornerstone of corporate governance, will lead to better monitoring of the performance of the director, including his obligation to observe conservative practices to protect the interests of shareholders and creditors. The present study aims to investigate the effect of corporate governance mechanisms on accounting conservatism in listed companies in Tehran Stock Exchange. The research hypotheses were tested using a sample of 645 observations of the companies between 2012 and 2016 using a multiple regression model based on panel data technique. The findings show that the size of the board, the percentage of institutional ownership and the amount of free float have a significant effect on accounting conservatism, while the percentage of ownership of the board does not have a significant effect on accounting conservatism.