This paper investigates whether branch network sizes of regional banks influence their management performances positively under the region-based relationship banking policy. Specifically, the effect of branch numbers of regional banks on their credit businesses and profits are empirically examined. As a result, it was found that regional banks with more branches can increase their loans and bills discounted as well as their small and mid-sized enterprises (SME) loans and bills. Thus, establishing more branches is effective in increasing the sum of loans and bills discounted of each bank because regional banks with many branches can come in contact with more customers. On the other hand, it was found that return on assets (ROA) and return on equity (ROE) of regional banks with more branches are lower. When we focus on the cost performances of regional banks, establishing too many branches and keeping branch networks that are too large might have negative effects on regional banks.