64 страниц. 2012 год. LAP Lambert Academic Publishing This study is aimed to determine the role of ownership structure on firm performance. Using panel data regression analysis method, the role of variables of ownership structure which includes: ownership concentration, institutional ownership and institutional ownership concentration have been examined for 137 listed firms of Tehran stock exchange within the period 2001 to 2006. The findings of this research shed light on the role of ownership structure plays in corporate performance and thus offer insights to policy makers interested in improving corporate governance system.