With education reform advancing, goals are shifting toward competency-based approaches, making the use of Pedagogical Content Knowledge (PCK) to enhance primary school teachers’ professional development a key challenge. The Sports Administration of the Ministry of Education has developed a Physical Education Instructional Module based on the 12-Year National Basic Education Curriculum Guidelines, designed to be simple and user-friendly with a competency-based approach. However, how to effectively utilize these modules to promote teachers’ continuous professional development remains an important issue that requires in-depth exploration. Therefore, the purpose of this study is to explore the professional development of primary school teachers in competency-based physical education instruction through the use of the Physical Education Instructional Module. Methods: The study participants were six physical education teachers from a primary school in New Taipei City. Each teacher implemented six lessons using the Physical Education Instructional Module. Data were collected through meeting minutes from domain meetings and semi-structured interviews. The data were analyzed using categorical aggregation and constant comparative analysis. Results: 1. Teachers showed improvement in their understanding of competency-based teaching concepts through participation in professional development; however, outcomes varied depending on the teaching perspectives held by the teachers. 2.Teachers implemented the Physical Education Instructional Module and recognized it as one method for designing competency-based instruction. 3.When teachers used competency-based physical education instruction, students experienced integrated learning that was more aligned with the development of core competencies. Recommendations: 1. The implementation of the Physical Education Instructional Module for school-based competency-based physical education practice requires the support of a guiding system; 2. There is a need for more in-depth exploration into how to design ongoing professional development methods that support teachers in engaging with school-based competency-based physical education.