Banking sector, as in many countries, has the largest share in the financial market in Turkey. Increasing competition conditions has forced banks to work more effectively, especially after the liberalization process in the 1980’s. Within this framework, the aim of this dissertation is to investigate the cost and profit efficiency of the commercial banks operating in Turkey. The dissertation is organized as follows. Firstly, the concept of efficiency is clarified and then the efficiency measurement methods are introduced. Secondly, the historical development of the Turkish banking sector, to related years, are presented. Finally, in the framework of the intermediation approach, panel data belonging to 32 commercial banks operating between the years 2003–2007 is used and the efficiency scores of banks are calculated by estimating the stochastic translog cost and profit functions. The main reason for choosing this period is the studies about this period are not enough and external shocks like crises didn’t occur after the transition to inflation accounting since 2003. As a result of the study, it is evident that the small-scale and foreign banks in the Turkish banking sector operate more efficient than other banks in terms of both profit and cost. Especially, the low efficiency level of state banks is associated with the size of banks and managerial skills.