Capital structure policy is a mean to tradeoff between risk and return and many factors influencing the optimal capital structure for each company. The aim of this study is to investigate the factors affecting the capital structure of companies listed in Tehran Stock Exchange and some selected stock exchanges in the developed and developing countries, and compare these determinants in a domestic versus international setting. Determinants of capital structure, considered in this research, are in the firm and country levels. In the firm level, profitability distance from bankruptcy, size and the ratio of fixed assets to total assets are used, and in the country level, the role of country’s GDP growth and stock market development is investigated. For international companies, we used Compustat Global Vantage database and World Bank databases and for domestic companies, we used Tadbirpardaz database to collect data. The findings showed the determinants significantly effecting on capital structure in four populations: the whole world, developed countries, developing countries, and Iran. Finally, we found that the developed and developing countries profitability and the size have different effects on capital structure. Alternatively in comparison between Iran and the developed countries, size and the ration of fixed assets have different effects on capital structure.