This study aims to examine the relationship between corporate governance and corporate economic performance, regarding the moderating effect of firm size. To test the hypotheses, multivariate OLS method was used. The data consists of 118 companies listed in the Tehran Stock Exchange in the period 2010 to 2014, and totally 708 company-years. The findings showed that corporate governance and corporate economic performance are positively correlated, and that firm size may enhance this relationship.