This paper aims to conduct an empirical analysis to determine whether the cost-reduction efforts, such as branch closures, actively pursued by domestic banks during the restructuring process following the foreign exchange crisis actually led to improvements in branch efficiency, and to identify the factors that determine bank branch efficiency. For this purpose, the cost and revenue efficiency of branches were estimated using DEA (Data Envelopment Analysis), a non-parametric estimation method, targeting 351 branches of a large domestic bank with an extensive nationwide branch network. Efficiency analysis by customer-segment branch groups was also conducted to analyze efficiency differences based on branch customer structures. The data used covered semi-annual branch balance sheet and income statement data from the first half of 1999 to the second half of 2000, a period when the effects of the foreign exchange crisis had begun to stabilize. The empirical results showed that the average revenue efficiency of bank branches declined statistically significantly from 0.839 in the first half of 1999 to 0.802 in the second half of 2000, and the average cost efficiency also declined statistically significantly from 0.907 in the first half of 1999 to 0.830 in the second half of 2000. These results indicate that during the implementation of uniform restructuring after the foreign exchange crisis, the efficiency gap between branches actually widened, resulting in an overall deterioration in both revenue efficiency and cost efficiency of bank branches. By branch group, corporate-client specialized branches exhibited the lowest revenue efficiency and the highest cost efficiency among all branch groups, while individual-client specialized branches showed high revenue efficiency but low cost efficiency, presenting a clear contrast to corporate-client specialized branches. Additionally, this paper tested the efficient structure hypothesis by analyzing whether efficiency has a significant effect on profitability in the domestic financial market. The results showed that efficiency does have a significant effect on profitability in the domestic financial market, confirming the importance of efficiency research and strategy formulation based on it. Furthermore, regression analysis was conducted to examine which factors affect efficiency in order to derive useful implications for formulating effective bank branch strategies. Through the regression analysis using financial characteristic variables of bank branches as explanatory variables, key financial characteristic variables related to improving bank branch efficiency were identified.