This study has a following hypothesis: If the world citizenship education would be made for retired senior adults to participate in international cooperation activities abroad as a volunteer, it will be able to make more meaningful activities and richer experience for them. First of all, this study is to explore the meaning of the experience of the senior volunteers who participated in the international development cooperation activities. In addition we intend to view the global citizenship education required to those seniors in a viewpoint of adult education. Therefore, research questions of this study are as followings. First, what is their level of global citizenship dispatched without world citizenship education. Secondly, what global citizenship education for facilitating their inward change may be desirable. For this purpose, this study utilized the phenomenological method as a qualitative research through in-depth interviews about their experiences. The results of the interviews were derived five kinds of sense elements in this study. There are , , , , . The choice of activities abroad was the challenge of their second life senior volunteers personally, and the experience gained in special activities was acting in the sense of a new life for them. In short, a volunteer abroad was learning through experience for them. And it was enough to reach self-realization experience or a sense of euphoria experience learning has given great significance to them. But accidental self-learning gained from the field of experience, which means overseas volunteer, has limitations and possibilities for adult education at the same time. For instance, they accidentally became themselves global citizens abroad naturally through a learning experience achieved by self-learning. However, if they have been able to participate global citizenship education in terms of adult education in advance, the experience of volunteering abroad would have been able to expand the meaning of life in another dimension to them.