Abstarct: The purpose of this study was to investigate the effect of operational inflexibility and degree of operating leverage on the degree of financial leverage and to explain the mediating role of operational inflexibility on the effect of degree of operating leverage on the degree of financial leverage in companies listed on the Tehran Stock Exchange. The statistical sample of this research is 180 companies and time domains in the period of 1395 to 1399 and in order to classify the data, EXCEL software has been used and for modeling and data processing, EViews software has been used. The dependent variables of the research are the degree of financial leverage and the independent variables of the research are operational inflexibility, the degree of operational leverage, the ratio of bank loans and the ratio of short-term debt. The control variables of the research are: cytobin, return on assets ratio and fixed assets ratio. In order to test the research hypotheses multiple regression method has been used. According to the obtained results, a positive and significant effect of operational inflexibility and the degree of operational leverage on the degree of financial leverage is observed. The results also indicate the mediating role of operational inflexibility in the effect of operating leverage on financial leverage. According to the obtained results, the greater the operational flexibility in the company, the greater the effect of the degree of operational leverage on the degree of financial leverage. The results also show the positive effect of the bank loan ratio variable and the negative effect of the return on assets ratio on the degree of financial leverage.