The aim of this study was to explore and compare primary student teachers (PSTs) pedagogical content knowledge (PCK) about teaching changes in matter. In order to determine the PSTs conceptual understanding of changes in matter, a multiple choice test, open-ended questions were administered and followed by semi-structured interviews to determine and compare pedagogical knowledge of PSTs. This study was carried out with primary student teachers at the University in southeast Turkey. The results of this study showed that more than half of PSTs have developed appropriate conceptual understanding of changes in matter as their content knowledge. Last grade student teachers had slightly better subject matter knowledge than 3rd grade ones in terms of plausible and appropriate answers. The study also revealed that 3rd grade student teachers had slightly better pedagogical knowledge consisting of knowledge of curriculum, learning difficulties of the students and instructional strategies than last grade ones.