The purpose of this study is to develop an in-service teacher training program for professional development in environmental education. In order to achieve the goal, the in- service teacher training program for professional development in environmental education development / implement team is formed to deal with the development and the implementation of the program. The team is composed of environmental education professionals and environmental education teachers. After the development of the program, 20 teachers were selected to implement the program. Then, through various researches such as interview, monitoring, and survey, the evaluation of the program was done. After the evaluation, the feedback on the program was collected in order to apply the final adjustments and changes to the developed training program for professional development in environmental education. The training program is designed to include the wide range of theories and real life cases. It focuses on certain topic, and is implemented through workshop type training method to increase the participation rate. The major motive of the participants was to develop their professionality in environmental education. Based on the analysis of the training program and the workshop, 69.1% of the program is focused on the environmental education/learning theory, and 71.4% is focused on the environmental education teaching method. The environmental education teaching method is focused on the real life teaching method that could be used in many schools. However, the parts on environmental education philosophy, psychology, and evaluation was not included as a part of the program. Also, the evaluation method of the students learning the environmental education was not introduced as a part of the program as well. It is due to the limited time frame of the training program, as well as its focus on the training method of environmental program. Based on the analysis of the evaluation results obtained through monitoring, the training program for professional development in environmental education is successful in terms of focusing the goal of the program around the environmental education/learning theory and environmental education teaching method, which was the motive of the participants. However, the effectiveness of the program differed from participants to participants based on their majors in environmental education, and it did not last long enough. The future training program for professional development in environmental education should consider the backgrounds of the program participants to have various programs prepared for various groups of people. We suggest that the results of this developed program will be applied to "environmental education teacher licence training" in the future.