The purposes of the present paper are threefold: To identify and analyze key success factors for the successful transfer of the human resource management (HRM) systems of Korean firms to the subsidiaries operating in Thailand; to find the determinants of the similarities between HRM systems of the mother companies in Korea and those of the subsidiaries in Thailand; and to investigate the evolving process of HRM systems in the subsidiaries over time. For these purposes, we visited eight subsidiaries of Korean firms operating in Thailand and had interviews with presidents and HRM managers. For the first purpose, we developed a model about the dual structures of management and institutionalization process of management practices. Those firms that understood the core values and guiding principles behind HRM practices had more successful transfer processes. There may be some changes at the policy, but not acceptance level. Internalization process, beyond implementation, was necessary for the successful institutionalization of HRM practices in Thai subsidiaries. For the second purpose, we identified global HRM strategy, strategic roles of foreign subsidiaries, and investment types as some determinants of the similarities of the two HRM systems. Unexpectedly, there was little variation in similarity. Finally, we suggested and analyzed two sets of hypotheses (i.e., economic rationality factors and institutional legitimacy factors) in explaining the evolving process of HRM systems, and found both factors influenced the process. Overall, we found some differences in the localization process between Western firms and Korean firms. While most Western firms went through plan-do-see process, Korean firms mostly experienced do-see-plan process. In addition, Korean firms pursued the maximization of organizational capability through individual competences, rather than the other way round. Some theoretical and practical implications were derived.