The aim of this study was to explore the ways in which the recent discussion on global citizenship education could contribute to the discursive possibility of education that addresses cultural diversity and co-existence which had not been considered much in the education for sustainable development (ESD) field. For that, the study showed how the formative experience of global citizen identity as the core concept of global citizenship can be a significant learning experience for ESD. The case studies included UNESCO school activity, school club activity, international volunteering activity and local cultural exchange activity. Based on the interviews with participants, the study found out that they were in the state of accepting or orienting themselves toward global citizen identity. The study also identified the kinds of qualitative experiences affecting such identity formation as facing and reflecting on one’s own cultural bias, intercultural sympathy, participation and action beyond mere knowledge acquisition, self-directed participation and achievement, lack of reflection in the one’ own life context as a global citizen, and conflict with the values embedded in the competition-driven lifestyle. Based on the result, the potential and meanings of the ESD focused on global citizen identity were discussed.