The purpose of this research is to identify a mediating effect of change management activity(CMA) on the relationships between the role of participants of ERP implementation and system performance. In this paper the role of participants are composed of top`s management, user`s participation, project manager`s skill. Also this research organized ERP system performance into the three dimensions(adaptation to the end-user`s ERP system, system usage, individual`s performance). The major results of this research can be summarized as follow; project manager`s role, top management`s involvement, and users` participation in ERP project directly affect CMA of system implementation process and have influence system performance through CMA too. CMA also has a positive effect on a series of system performance, that is, adaptation to the end-user`s ERP system, system usage, and individual`s performance. In conclusion, the role of participants have an considerable influence upon system performance through CMA. This research makes certain that a mediating effect of CMA between the role of participants and system performance exists. Therefore, the companies implementing ERP must consider CMA.