This paper discusses the Inter-Regional Cooperation based on Endogeneous Development that take place in three places located in Northeast Tochigi Prefecture; Kuroiso City, Nasu-machi, and Kurobanemachi. In the beginning, it research the local residents' wishes through the fieldwork and interview survey. This research planned the common theme,"Suijunkyc (water circulate homeland) that nurtures, flows and creates life", which the"water"as the one of main natural resources that holds the area together. According to the theme, the area can be considered as three"Sato", which exist together as a livelihood system. And they are not constrained by usual administration system. The three"Sato"means"Sato where the water begins","Sato where the water gathers",and "Sato where the water flows"and set the activities that reflect each concept of space. The area exist as a whole activities of each space and the local cooperation accomplished beyond common administration reel. The regional cooperation beyond the administration reel is achieved by basis of the endogeneous development theory. Furthermore, this cooperation become an efficient strategy to make a sustainable society in future.