<p>This study empirically explored the possibility of nurturing and cultivating reflexivity capacity at the small-group level through cross-cultural online citizen dialogue on biodiversity conservation and citizens’ role using a method of reflecting, connecting Taiwan and Japan. The study found that cross-cultural dialogue improved self-awareness of cultural inheritance as a hindering and promoting factor for sustainability transformation in one’s own cultural community. The dialogue also expanded the perceived boundary of collaboration measured by trust score/ratio. It also brought about the positive change in self-reported attitude toward dialogue with a person holding different views, and of urgency/significance self-assessment of sustainability transformation issues, that is, biodiversity conservation and citizen participation. The institutionalization of cross-cultural citizen dialogue in collective decision-making processes, such as those of the United Nations, and reflexivity capacity building, both at the small-group and population levels through citizen dialogue connecting different cultural groups, are suggested for sustainability transformation.</p>