The primary focus of this study is the use of portfolio development in an in-service teacher education course that aimed to help primary school teachers develop a better understanding of, and ability to implement, an innovative teaching approach--namely, task-based learning (TBL)--in Chinese language. It explores the impact of portfolio development on teachers' understanding of TBL and their views on portfolio development. The research employed a combination of quantitative and qualitative methods, with data being collected through questionnaires and interviews. The findings showed that the portfolio development had a positive impact on teachers' understanding of, attitude to and confidence in applying TBL. The processes encouraged teachers to think through their practice, to become more conscious of their teaching. On the basis of the major results, this study suggests improvements for the future use of portfolio development for in-service teacher education courses and for teachers' professional development. (Contains 1 note and 3 tables.)