Collaborative lesson preparation is a common practice for Chinese teachers who work together to solve their teaching difficulties and problems. Based on the theoretical framework of community of practice (CoP), this paper describes how a teaching group in a university (entitled G University) in China was engaged in its lesson-preparation community and how the collaboration in lesson preparation impacted teachers' professional development. Based on the findings of the study some lessons have been drawn about how to establish a successful CoP to promote Chinese teachers' professional development.