Due to rapid urbanization progress and growth of sense of citizen autonomy, the necessity of participatory urban planning is now getting more emphasized than the past. In particular, community organizations which residents independently form have served as a starting point for encouraging participatory planning and provided people with a guideline for diverse community activities. Japan the country which has developed very successful Machizukuri planning system - has supported expansion of public participation and diverse community activities in the urban planning field. These community organizations now become a major part of Machizukuri and supplements administration services, so the demand for developing these organizations is gradually increasing in Japan. Kagurazaka district in Shinjuku, Japan is the area mixed with urban residential and commercial uses. This area has preserved its residential environment and effectively dealt with development pressure for a long time by forming community organizations. Considering this aspect, this study analyzes the transitional process of community organizations and their operational characteristics in Kagurazaka district. Then, this study conclusively suggests some implications on feasibility of Machizukuri activities through community organizations and strategies for successful management of community organizations.