Mathematics pre-service teachers (PSTs) engage in teaching practice under the guidance of mentor teachers during teaching practice. This qualitative study explores mentor teachers' perceptions of mathematics PSTs' preparedness to teach mathematics in primary schools. An interpretive paradigm was adopted, while a case study was employed as the research design. Twelve mathematics mentor teachers were sampled through snowball sampling from twelve primary schools in Kwa-Zulu Natal province, South Africa. Open-ended questionnaires were employed to generate data, and the data were analyzed thematically. This study found that teachers have diverse views about mathematics PSTs' preparedness to teach. Some mentor teachers expressed reservations about the preparedness of mathematics PSTs to teach while others were confident about mathematics PSTs' content and pedagogical knowledge. Although some mentor teachers expressed confidence in PSTs' pedagogical content knowledge, the study recommends that all mentor teachers should support PSTs to develop their mathematics pedagogical content knowledge.