ABSTRACT Proteins with high catalytic efficiency and selectivity under mild conditions have long been appreciated by industrial and medicinal fields. These proteins, which are commonly multimeric, often possess low stability, impeding wider application. Currently, strategies to improve the stability of multimeric proteins concentrate on enhancing the interaction at internal interface of the subunits. In this report, we confirmed that the largely underestimated subunit terminal ends are as significant as the internal interface for protein stability. By connecting both the terminal ends and internal interface of subunits, the tetrameric Leifsonia alcohol dehydrogenase ( Ln ADH) protein can been cyclized into a rigid form with significantly improved thermostability and resilience. The improvement in the temperature at which enzyme activity is reduced to 50% after a 15-min heat treatment ( T 50 15 ) and melting temperature ( T m ) of the modified protein was 18°C and 23.3°C, respectively, which is superior to the results achieved by normal protein engineering. Our study provided a novel strategy to effectively improve the stability of multimeric proteins, which is suitable not only for the short-chain dehydrogenase/reductase (SDR) family but also other classes of proteins with close terminal ends. IMPORTANCE Industrially interesting proteins are generally multimeric proteins; however, their applications are often restricted due to low stability caused by the natural tendency of subunit disassociation. Current approaches targeting this problem mainly focus on enhancing the internal interfaces of the subunits to avoid their disassociation. In this study, we identified and confirmed the external interface to be significant for improving the stability of multimeric proteins. By connecting the terminal ends and internal interface with disulfide bonds, we found that the multimeric protein Ln ADH cyclized into a robust monomeric-like form, resulting in superior thermostability compared to traditional protein engineering. This intersubunit cyclization approach is efficient and easy to perform, providing a novel method for engineering many important classes of multimeric proteins.