Merger is one of the efforts to increase the company's growth non-organically which requires large costs and better management capabilities. This study aimed to determine the impact of mergers on bank performance, which indirectly affects the bank health level. The subjects of this research were 12 conventional banks in Indonesia which have merged horizontally from 2007 to 2019. The variables in this study are those related to bank performance improvement, such as risk-based bank-rating ratio. The results show that there is no difference between bank performance, credit level, operational level, and capital level between before and after the merger. By conducting the merger, it turns out that the average bank performance does not have a positive impact, and this is related to the increase in credit level, operational level, and liquidity level, which are not aligned with an increase in market risk and bank capital level.