In-service language teachers' professional development is a crucial factor that influences the teaching and learning effectiveness. Educational action research is considered by many researchers and scholars as an effective way or approach for language teachers' professional development. This article reports a case study of in-service English language teachers doing action research within a collaborative action research project. The focus of the case study is upon investigating the problems and difficulties that English language teachers encounter in doing action research and some solutions to the problems are provided. This research sheds light on the practice and application of educational action research.