In this research, we compare and evaluate effect of corporate governance on performance of firms before and after issuing the audit committee’s instruction. To test hypotheses, we used systematic deletion method and selected 128 firms from the firms listed on Tehran Stock Exchange during the period from 2011 to 2016. To investigate the research hypothesis, multiple regression method was applied on the related data and the results showed that institutional ownership, management ownership, and independence of the board have a positive and significant effect on the firm performance, while concentration of ownership and size of the board have no significant effect on firm performance. Institutional ownership, management ownership, independence of the board of directors and size of the board have a positive and significant effect on performance of firms before announcing instructions of the audit committee, while, ownership concentration on firm performance before announcing instructions of the audit committee has a negative and significant effect. In addition, institutional ownership and management ownership have a positive and significant effect on performance of firms after announcement of instructions of the audit committee, while ownership concentration, board independence and board size have no significant effect on performance of firms after announcement of instructions of the audit committee.
