The purpose of this study is to develop School Agenda 21 to activate environmental education at schools. In detail, this study is intended to develop operating procedures, major issue areas or domains, and instructions on the preparation for School Agenda 21. School Agenda 21 means the action plan which students, teachers, parents, and other concerned parties (including office of education, local municipal bodies, and NGOs) write under agreement with respect to their respective roles in order to activate environmental educations oriented toward sustainable development. The results of this study are as follow. First, the operating procedures for School Agenda 21 consist of seven steps; organization, diagnosis of problems, setup of targets or objectives, development of codes of behavior, system establishment, practices and reviews, and evaluation and feedbacks. Second, major issue areas for School Agenda 21 are classified into six; school management, class operation, independent subject activity, separate subject activity, non-subject activity, and external relations of school. Third, instructions of the preparation of School Agenda 21 address these 10 concepts; balance, unification, continuity, daily routine, linkage, environmental justice, participation, peculiarity of schools and classes, regional peculiarity, and concreteness, which consider 7 principles for environmental education, levels of learners, regional features, and concreteness. School Agenda 21 developed from this study converts existing environmental education toward sustainable development environmental education, and developed for the purpose to activate school environmental education, but ultimate purpose of this study are realizing sustainable society, sustainable future to realize education for sustainable development. So School Agenda 21 is expected to important performance way making possible Local Agenda 21, National Agenda 21, Agenda 21 as if education, public recognition and discipline contents of the 36 chapter of Agenda 21.