Efficiency plays essential role for improving the performance of banking industry. In this paper, we present an empirical investigation to study the effect of efficiency on abnormal return. The proposed study collects the necessary information from official statements as well as historical data over the period 2009-2013 reported on Tehran Stock Exchange to examine the relationship between efficiency and abnormal return. Using regression analysis, the study has determined a meaningful, positive but weak relationship between abnormal return and efficiency. However, the study does not find any meaningful relationship between bank size and abnormal return.