The main purpose of this research is to investigate the effect of CEO's power on capital structure in companies admitted to Tehran Stock Exchange. In order to investigate this, the research hypothesis was based on a statistical sample consisting of 92 companies during an 11-year period from 1384 to 1395 and tested using multivariable regression models. For this purpose, the leverage based on the book value and the market-based leverage are used as the capital structure representative. Also, the dual variables of the CEO's duty and the duration of the CEO's tenure were considered as the CEO's power representative. The results of this research show that the nonlinear relationship between CEO power and book value-based leverage is not statistically significant. In contrast, the nonlinear relationship between the CEO's power and the market-based leverage is confirmed.The results of this research show that the nonlinear relationship between CEO power and book value-based leverage is not statistically significant. In contrast, the nonlinear relationship between the CEO's power and the market-based leverage is confirmed.