In this research, the attempt is to see whether it is possible to associate the management forecast bias of earnings to conservatism accounting. In this respect, the net assets book value to their market value ratio (BTM) has been used as a measure for conservatism and the difference between actual earning and forecasted earning as a measure of management forecast bias of earnings. By using linear regression between two mentioned measures, it has been concluded that there is a positive associate between the level of conservatism and management forecast bias of earnings. Totally this result explains that conservative accounting acts as a substitution for the management forecast. In fact due to its nature of on time disclosure of bad news, the conservative accounting reduces the information asymmetric between the management and stockholders as well as legal risk of management. Therefore considering the conservative nature of accounting, there is less temptation for the management to deliver earning forecast in a way that is more accurate.