In Thailand, in-service teachers' professional development has been implemented through the Professional Learning Community (PLC) program for more than four years to develop teachers' sustainably. The sustainable development program has spread across the country in the Thai Teacher Council network. The research goals are as follows: (1) to evaluate the causes and results of the Professional Development Program in the form of a Professional Learning Community conducted by the Teachers' Council of Thailand and (2) to analyze factors affecting success and sustainability of the teacher professional development project. Within the study, 490 samples have been collected from the relevant parties. The respondents have completed the questionnaire and participated in the interview. The research results have revealed that the project is essential for teachers and education personnel. They change the teaching and learning approaches, as well as positive thinking skills; moreover, the students also increase academic achievements.