The aim of this study is to investigate the change of prospective mathematics teachers' pedagogical content knowledge (PCK) on the linear equation and slope subject based on the lesson plan development and implementation process based on the 4MAT model. The concept of PCK was discussed in three components as content knowledge, knowledge of student understanding and knowledge of instructional strategies. The research was carried out based on mixed research methods. The data collection tools consisted of 48 lesson plans developed by prospective teachers in three stages and observation notes taken based on the teachings they did. The lesson plans developed by prospective teachers were analyzed quantitatively using the rubric developed by the researcher. Whether there is a statistically significant difference in PCK components in the lesson plans was analyzed by using appropriate tests. In addition, various qualitative sections from the lesson plans showing the development of prospective teachers were presented. As a result of the research, it was concluded that prospective teachers showed improvement in each of the components of the PCK at the end of the lesson plan development and implementation process based on the 4MAT model.