The aim of the study is to investigate the contribution of action research to teachers' professional development. In line with this goal, a group of teachers were asked their opinions. The working group of the study is comprised of six teachers working at a state primary and middle school. The study is an example of "Case Study," one of qualitative research methods. The content analysis technique was utilized in the analysis of the data. To sum up, the teachers expressed that action research had a positive impact on their professional development in various aspects.