Recently, in Indonesia, project-based learning (PjBL) has been used as an alternative approach in the teaching and learning process. Research on PjBL has been widely conducted in many countries at various levels. In most previous studies, PjBL was used to improve students' competence in certain math subjects. This study uses a case study research method to determine the effectiveness of PjBL at university in improving pre-service teachers' PCK. The research was carried out in 2022 involving fourteen mathematics education study program students selected by purposive sampling. The instruments used consisted of observation sheets, tests, and questionnaires. During the PjBL activity, participants were given a project to develop teaching materials for geometric transformation using certain teaching-learning strategies. The results of the study show that PjBL can improve students' PCK ability, although participants face several obstacles related to commitment to completing projects on time. Therefore, PjBL can be applied in the teaching-learning process to support professional mathematics teachers.