In this study we have tried to analyze the impact of financial sector reform on the cost structure characteristics and on the ownership-cost efficiency relationship in Iranian commercial banking system. It also analyzes the impact of reform on dynamics of competition in lending market. Evidence shows that reform focuses on the banking regulation and deregulation. Therefore, deregulation induced competition should in turn translate into incentives for managers to improve efficiency and performance. On the other hand, the aim of prudential re-regulation is to foster stability and minimize excessive risk taking. In this study regulatory reform emphasizes on capital adequacy ratio. Estimation of the models performed by using data from 8 banks ( Meli, Sepah, Maskan,  Eghtesadnovin, Parsian, Melat, Tejarat and Saderat) for the period 1380-1389. The results show that the regulatory reform has a positive and significant impact on dynamics of competition in lending market. Our results also suggest that the ownership-cost efficiency relationship is affected by the reform and   regulatory reform as well as positive and significant impact on cost structure. Finally, regulatory reform has a positive impact on the efficiency cost within the mentioned period.

JEL Classification Codes: E52, E60