The purpose of this study is to analyze perceptions of competency development of participating teachers in the professional learning community (PLC) in schools. We conducted a survey among 1000 kindergarten to high school teachers who participated in the PLC in schools. In addition to the survey data, focus group interviews were conducted to acquire a more enhanced understanding of the survey responses. The survey questions included three areas : individual competency development, relationship competency development, and competencies related to school organization. The results revealed first that teachers perceived the effect of participating in the PLC on their as well as their peers’ competency development. as effective. Therefore, we concluded that participation in the PLC contributes to teacher competency development. Second, the participants perceived that participation in the PLC contributed more positively to relationship competency development than individual competency development. Third, of the competencies related to school organization, the development of competencies related to the spread of a democratic participation school culture, communication, and collaboration was perceived most positively. Fourth, the participants were less positive about individual development encompassing critical thinking and knowledge reconstruction. They also perceived competency development of leaders, including peer support and authority sharing, as less positive. Finally, the groups that participated in the PLC actively and voluntarily were more positive about the impact of PLC participation on teacher competency development in comparison to the other groups.