Peer teaching is a valuable practice that helps pre-service teachers to acquire the knowledge and the expertise required for teaching as well as improving their pedagogical content knowledge. For that reason, this study focused on the pre-service mathematics teachers' peer teaching, with the intention of exploring their pedagogical content knowledge as mirrored in peer teaching. The participants were four pre-service secondary mathematics teachers. Each participant designed a lesson plan and conducted peer teaching on a mathematics concept of her choice. The lesson plans and videotapes of the participants' peer teaching were the data collection instruments. The components of pedagogical content knowledge were used to analyze the data. The findings revealed that the pre-service mathematics teachers were knowledgeable about the subject content matter, but their knowledge of learners, understanding of instructional strategies and familiarity of context was inadequate about the topic of their peer teaching. The study recommends an amalgamated teaching of mathematics content courses and pedagogy courses.