Abstract: Organization development using team building is the use of technique, which can help improve and increase the organization efficiency because relationships between praetitioners and team building go on in the direction, which can promote and support one another. This research aimed to examine teamwork conditions at secondary schools in Thailand to develop a model of teacher team building at secondary school in Thailand and to evaluate the model of teacher team building at secondary schools in Thailand. The research consisted of these 6 stages. Stage 1 developed the conceptual framework and theory by examining principles and research works involving team building. Stage 2 examined teamwork of teacher at secondary schools using a questionnaire. Stage 3 examined teamwork of teacher at secondary schools using the focus group discourse technique. Stage 4 drafted the model of teacher team building at secondary schools. Stage 5 tried out the model of teacher team building at secondary school. Stage 6 evaluated the model of teacher team building. The results of research revealed the following: results of the study from examining teamwork conditions of teachers at secondary schools, it was found that the teachers had teamwork as a whole and in each aspect at a high level in this order from the highest to the lowest mean: team uniqueness, trust cooperation, working process, team meeting, organizational culture, motivation, participation, organizational climate, communication, decision-making, coordination, conflict management and leadership. The model of teacher team building consists of factors and process: factors of teacher team building: persons, work, team and school, process of teacher team building using the action research process consisted of these 5 stages: creating awareness of teamwork together at school cooperation in examining conditions of needs and teamwork problems at school cooperation in making the performance plan for teacher team building at school operation of teacher team building at school using the intervention and operation in evaluating the model of teacher team building. Results of evaluating the model of teacher team building at secondary school, there are the following 2 issues of evaluation: For evaluating appropriateness of the model as a whole, it was found that the model of teacher team building at secondary school had appropriateness at a high level in every aspect. In evaluating implementation of the model there are the following 20 issues being evaluated.