Investigating the Effect of Competitive Strategies on the Competitive Power Growth of Listed Companies in Tehran Stock Exchange - Comparison Pre-Sanction with Sanction Period Models Davood Moradi MSc., Department of Accounting, Faculty of Economics and Management, Urmia University, Urmia, Iran. E-mail: st_d.moradi@urmia.ac.ir Farzad Ghayour *Corresponding Author, Assistant Prof., Department of Accounting, Faculty of Economics and Management, Urmia University, Urmia, Iran. E-mail: f.ghayour@urmia.ac.ir Gholamreza Mansourfar Associate Prof., Department of Accounting, Faculty of Economics and Management, Urmia University, Urmia, Iran. E-mail: g.mansourfar@urmia.ac.ir Abstract Objective: The widespread competition in market, has forced companies to adopt strategies to deal with this competition. This study aims to investigate the effect of competitive strategies of product differentiation and cost management on growth of companies' competitive power and to scrutinize pre-sanction and sanction periods in regards with this effect. Methods: The sample consisted of 137 listed companies in the Tehran Stock Exchange during the years 2004 to 2015. Then research hypotheses analysed for three time periods namely pre-sanctions period (2004 - 2009), the sanctions period (2010 - 2015) and the whole period of 2004 - 2015 seprately. Results: The results showed that non of competitive strategies product differentiation and cost management had significant impact on the companies competitive power growth in the pre-sanctions period. The use of cost management and product differentiation strategies has led to increas and decrease in competitive power growth of companies respectively during the sanctions period. In addition, during this period, the intensity of the effect of product differentiation strategy on decreasing the competitive power growth has been more than the intensity of the effect of cost management strategy on increasing the competitive power growth. So, the effect of competitive strategies including product differentiation and cost management on growth of companies' competitive