SUMMARY
Managers tend to invest inexpressibly in projects to increase their profit, whether the project is profitable or not because the main desire and objective of managers are using resources for personal gain. Therefore, over investment reduces company performance and shareholder value. In this research, the impact of institutional investors on the relationship between over investment and performance of listed companies in the Tehran Stock Exchange was evaluated. In this regard, the collected data for 136 companies listed on the Tehran Stock Exchange during the years 2008-2014 were studied. The required data for hypotheses testing were extracted from Tadbir Pardaz software. In addition, financial statements of companies were derived. After preparing data in Excel software, hypothesis testing and analysis were performed by SPSS statistical software. The results of hypothesis testing showed that over investment and institutional ownership have respectively negative and positive significant relationships with the performance of companies listed on the Tehran Stock Exchange, but institutional ownership has not a significant impact on the relationship between over investment and the performance of companies listed on the Tehran Stock Exchange.