Abstract In this article, motives of Related Party Transactions are examined based on the model provided by Moscariello (2010). Previous literature has developed two contrasting theories, conflict of interests vs. efficient transactions hypothesis, to describe the reasons behind RPTs. However, the empirical evidence collected so far does not offer a unique answer, lacking to show a definite picture about the nature of similar transactions. If there is opportunistic behavior, there should be special relations between the amount of RPTs with ownership concentration level, market value to book value ratio, board size, percentage of nonexecutive board managers, Duality, and leverage. Research is performed over the years of 2006 to 2010 among Tehran Stock Exchange (TSE) listed companies. Test of hypothesis shows that there are significant expected relations between ownership concentration level, percentage of nonexecutive board managers, and leverage with the amount of RPTs. The empirical analysis, supported by the development of the theoretical model, points out the existence of an opportunistic behavior by the controlling shareholders.