The results of the research showed that there is a negative and significant relationship between managers' narcissism and financial performance (measure of asset return and company's market value) that these results confirm the financial-behavioral theory, which means that usually managers with high narcissism systematically lower future returns due to He overestimates the investment projects and overestimates the effect of favorable events on the company's cash flows and underestimates the probability and effect of unfavorable events on the company's cash flows. Therefore, managers with overconfidence usually have higher capital expenditures. and have weaker financial performance, and the results of this research also confirm that the narcissism of managers causes a decrease in the financial performance of companies. Also, the results showed that the presence of a powerful board of directors on one hand increases financial performance and on the other hand it moderates and reduces the negative relationship between managers' narcissism and financial performance of companies, which indicates the supervisory role of these managers in line with agency theory. And the corporate governance mechanism is strong. In other words, by increasing the independence and the size of the board of directors and the amount of ownership of managers, the opportunistic behavior of CEOs and their narcissism and unilateral and arrogant decisions are reduced, and as a result, the stock value and financial performance of the company increases. This result means that the role of a powerful board of directors in Iran is in accordance with the agency theory and the ability of this supervisory tool to reduce opportunistic behavior and behavior caused by narcissism and false self-confidence of CEOs is strong.