Project-based learning (PBL), a learning-by-doing practice, has been used for enhancing English as a Foreign Language (EFL) students' language skills. However, the extent to which and how EFL teachers develop or improve Computer-Assisted Language Learning (CALL) competencies while experiencing PBL remain unexplored. For this study an 18-week PBL project was designed to improve EFL teachers' CALL competencies. A total of 12 EFL prospective teachers were recruited to participate in a sequence of activities: class observations, group discussions, and the design of lesson plans. Pre- and post- TPACK (technological pedagogical content knowledge) surveys were administered to measure participants' improvement of CALL competencies. Qualitative data, including class observation notes, lesson plans, group discussion records, and reflective essays, were collected to triangulate and complement survey results. The survey results showed that the prospective teachers demonstrated higher levels of CALL competencies after the PBL project. Using the qualitative data, this study explicitly documented the benefits which prospective teachers may obtain and the problems they may face when participating in a PBL project. The findings can help future teacher educators understand how to design and implement effective teaching training for CALL competency development.