In this research, the impact of product market competition has been investigated on the relationship between ownership structure and the performance of companies accepted in Tehran Stock Exchange. The Performance has also been used with the criterion of market value to the book value of asset as the performance evaluation index. The statistical population of this study was the companies listed in the Tehran Stock Exchange for the time period of 2008 to 2014. The multivariate regression with virtual variable has been used in order to test the hypotheses. The results indicate that managerial ownership in a strong competitive environment has a significant effect on performance. While institutional ownership has a significant effect on performance under weak competitive conditions.
