Throughout the world, educational leaders are pushing for a movement away from teacher-directed learning to engaging students in student-driven learning. Project-based learning (PBL) has been adopted as an instructional approach that promotes student inquiry and cognitive growth. At the national level, Taiwan has launched a curriculum reform to encourage PBL-type learning opportunities for students. This study draws on the Teaching and Learning International Survey (TALIS) of 3,835 lower secondary teachers to investigate the degree to which Taiwan teachers engage in PBL. We identify influential factors for PBL using "the form" rather than "the content" of professional development and consider self-efficacy as a moderator to examine if the effect of professional development on PBL varies in teachers with different self-confidence in professional competence. The result indicates that teachers do not engage in PBL teaching strategies regularly. However, certain types of professional development do predict PBL practices, and self-efficacy is a significant moderator of this relationship. Professional development should attend to the advancement of teacher self-efficacy, primarily focusing on fostering capabilities of managing classrooms so the impact on teacher pedagogical practice can be greater. Additionally, school leaders should provide experiential learning and create enabling environments to sustain teachers' drive for innovative teaching strategies.