Tax evasion is a value-added activity that transfers wealth from the government to shareholders and limits corporate tax payments. On the other hand, tax evasion can be a shield to divert managers' interests. The main purpose of this research is to identify the existence of The relationship between tax evasion and debt expense in companies listed on the Tehran Stock Exchange is. And whether the level of institutional ownership as a form of ownership moderates this relationship. Therefore, in the present study, the effect of ownership structure on the relationship between tax avoidance and debt expense in companies listed on the Tehran Stock Exchange has been investigated. For this purpose, a sample of 111 companies active in the Tehran Stock Exchange including a seven-year period based on the financial statements of the companies studied during the years 1390 to 1396 was selected and to test the hypotheses using multivariate linear regression method with Using EVIEWS software version 9, was used. The results indicate that there is a significant and direct relationship between tax avoidance and debt cost and the effect of concentration of ownership and institutional ownership on the relationship between tax avoidance and debt cost was not statistically confirmed.