Banks have an important role and contribute substantially to the growth and progress of the national economy. Therefore, several researches have been conducted to examine their performance using Data Envelopment Analysis (DEA). However, in most of these researches relatively little attention has been paid to the choice of variables. While changing of input and output variables causes the efficiency scores of decision making units to differ very much, it does also affect the resulting evaluations. Consequently, in this article, the technical efficiency of 10 Iranian commercial and specialized banks will be measured by using a systematic approach called "stepwise DEA". The results of using this approach indicates that the three main variables of the model are: fixed assets, number of employees and partnerships and direct investments. And the three efficient banks were identified.