Abstarct: Banking sectors throughout the world have witnessed significant developments over the last three decades as changes in the environment in which they operate have had substantial implications for their business activities. Deregulation, globalization, financial innovation and technological progress all have gradually reduced the costs of information processing and transmission and have been major forces impacting on the performance of the international banking sector.Given this, there is a pressing need to investigate and measure the impact of various macro-economic factors and/or institutional policy changes on banks’ performance as this type of analysis will assist government instrumentalities and banking regulators in policy choice. It will also enable bank management to improve the way in which they allocate resources across the various investment opportunities available to them. In the traditional cost efficiency DEA model (Fare et al,1985), it is assumed that input prices are the same across all decision making units (DMUs). However, actual markets do not necessarily function under perfect competition and unit input prices might not be identical across all DMUs. Thus, as pointed out by Tone (2002) the traditional DEA cost efficiency model does not take account of the fact that costs can obviously be reduced by reducing the input factor prices. This study estimates cost efficiency by using the New DEA model (Tone,2002), for Saman bank branches in province of Tehran over the period 2011-2015. The results obtained in the case study showed that the DEA models can provide robust estimates of cost efficiency even in situations of price uncertainty.