Despite its severiti and deep influence on both the real and financial sectors empirical evidence on the evolution of the performance of the ASEAN-4 banking sectors since the 1997-1998 Asian finencial crisis is relatively scarce. By employing the data enfelopment Analysis (DEA) apporach the present study examines for the first time the impact of the Asian financial crisis on the efficiency of the ASEAN-4 countries banking secters. This study focuses on to major approaches vis. Intermediation and revenue approaches. The empirical findings seggets that the estimates of technical efficiency are costitenly higher under the revenue approach. We find that banks are relativelly inefficient in a more concentrated banking market. However when we control for countries that participate in IMF program the concentrated latio exhibits a positive relationship with bank efficinci levels inplying that the mor concetrated banking syistem which parcitipates in IMF program is relatively more efficient in their intermediation function during the post crisis period.