The professional development of teacher is an indispensable requirement for a quality education system. This has been demonstrated not only by global innovative education but also by Vietnam’s educational development trends. This study was conducted among 293 teachers and managers at high schools in Vietnam. It aims to explore the formats that teachers used to improve their professional development, the frequency of using these formats and teachers' self-assessments about their impact on professional developments. The findings revealed that high school teachers involved themselves in reading, and conducting or participating in research. Teachers expressed their view that professional development based on school's characteristics or on creating a learning community within a school had the highest impact on professional development.