This study is aiming to exploring the related issues about the action research applied to teacher professional development. The main objectives explore (l) the motives, difficulties, advantages of teachers applying the action research, and (2) the importance, meaning, application, advantage of applying action research, to teacher professional development, and (3) the methods of school helping or encouraging teachers applying the action research. The main methods applied in this study is in-depth interview in order to understand the reason of teachers applying the action research, and the influence of applying to professional development. The conclusions of this study shows that it is advantageous that teachers apply action research to improve the professional development and solve the practice problem. The difficulties of applying the action research are time and resource. In order to apply the result of action research most, it is recommended to announce the result publicly.