The present study is an action research on preservice teachers' collaborative inquiry. As a teacher educator, I found the individualistic and competitive approach to preservice teacher education problematic. A great number of studies have shown that teacher collaboration has a positive impact on professional development and leads to improvement in teachers' knowledge and practice. To facilitate collaborative professional development among preservice teachers, I conducted this action research. I developed a collaborative inquiry model for preservice teachers based on the concepts of 'knowledge-of-practice', lesson study, and microteaching and implemented it for one semester in a preservice teacher education program. The collaborative inquiry model consists of a cyclic process of collective planning, teaching and observation, evaluation and feedback, self-reflection, revision and re-teach. The results of this study showed that the collaborative inquiry model was of help to improve preservice teachers' professional knowledge and practice. Based on the results, how to effectively foster preservice teachers' collaborative professional development was discussed.