This study examines the effect of capital structure and ownership structure on Firm's performance using sample of 123 companies listed on Tehran Stock Exchange (TSE) during eight-year period, 2001-2008. We adopt rate of return on assets as a measure of firm's performance. The research results show that capital structure and ownership structure have a positive impact on the performance of companies listed on TSE. This study indicates consistency with prior empirical researches and also all research subsidiary hypotheses are consistent with the theoretical assumptions and all of them have been approved.