Abstarct: The ability to participate in identifying potential domestic and foreign resources to provide capital for investment and planning is considered as one of the main factors behind the growth and development of any company. To optimize the capital structure, it is important to recognize the various sources of finance and the costs involved in deciding managers to maximize the value of the company. Variables and factors can influence the profitability and efficiency of an enterprise by influencing the selection of optimal capital structure. Therefore, the study of the effectiveness of the structure of corporate finance resources (capital structure) from different parameters, including internal characteristics and the type of activity and external and environmental factors of companies can determine the position of companies in financing markets and managers And investors are aware of the threats and opportunities available. In fact, in this research, we have tried to study the impact of some of the company's features such as profitability, company size, growth opportunity, liquidity and visible assets, as well as some environmental and external factors such as inflation and interest rates in determining the optimal capital structure. To collect information, financial managers, investors and lenders can use their results in their decisions. For this purpose, a total of 97 active companies in Tehran Stock Exchange during the years 1385-1395 were selected by sampling method as a sample and analyzed by using time-series regression (panel data). The results of the research show that the size of the company, the tangible assets, the opportunity of growth and liquidity have a Direct and significant relationship with capital structure And profitability, inflation rate and interest rate have a reverse and significant relationship with it.