The purpose of the research is to explicate self-organization process in the organizational conversion from a corporation to a co-operative. The authors conducted a case study focusing on self-organization through the participant observation of Happy Bridge Co-operative (hereafter HBC). The results are as follows: First, converting a corporation to a co-operative is the outcome of highly complex interactions. It is a very dynamic process of conflict between two different organizational principles, i.e., association and business, and is also a strategic choice for the organization renewal. Second, after conversion to co-operative, the new dynamics has been created in the process of adaption to co-operative principles and systems. Third, the hidden conflicts within the organization have been gradually emerged and materialized. In this process, HBC has been able to find the new opportunities for innovation nevertheless it is likely to face further conflicts and contradiction promoting innovation. Becoming a co-operative is not only the changes of ownership structure, but also the fundamental transformation of organization. The management of HBC cannot lead new innovations, and the members cannot completely learn new routines. Theoretically, this study explains how self-organizing process makes co- operative conversion viable by means of continuous change. And we can suggest practical implications that converting process of co-operative provides new chances of innovation through the self-organizing process.