This study explores the influences of problem-based learning (PBL) on 21 elementary school pre-service English teachers' pedagogical content knowledge in a teacher education programme in a university in northern Taiwan. This study has the following major findings based on the analysis of final projects, videos, and interviews. First, participants regarded lesson planning and making teaching aids as their professional learning in pedagogical content knowledge. Secondly, participants regarded 'field experience' and 'the university instructor's facilitation' fostered their pedagogical content knowledge development through PBL.