The aim of this study is to examine the relationship between the reflective thinking levels of secondary school mathematics teacher candidates and their philosophical thoughts about the nature of mathematics. In addition, it was also aimed to examine whether the reflective thinking levels of pre-service mathematics teachers differ significantly according to the absolutist, mixed and quasi-experimental groups. For this purpose, the relational survey model was used in the research. The research was carried out with 196 volunteer secondary school mathematics teacher candidates studying in the mathematics education program in the spring semester of the 2021-2022 academic year. At the end of the study, it was determined that both the reflective thinking levels of the mathematics teacher candidates and their philosophical thoughts about the nature of mathematics were at a high level. In addition, it was determined that there was a moderately significant positive correlation between the sub-dimensions of the reflective thinking levels of pre-service mathematics teachers and their philosophical thoughts about the nature of mathematics, which explained 44%. In addition, it was determined that the reflection sub-dimension predicted the prospective teachers' philosophical thoughts on the nature of mathematics positively, and the habit sub-dimension statistically predicted negatively. Finally, it was concluded that there is a statistically significant difference between the quasi-experimental group, mixed and absolutist groups in favor of the quasi-experimental group in the critical reflection, reflection and comprehension skills of the secondary school mathematics teacher candidates, and in the habit sub-dimension, there is a statistically significant difference between the absolutist group, the mixed and quasi-experimental groups in favor of the absolutist group has been reached.