The purpose of this study is to develop a highly valid and reliable scale which determines pre-service mathematics teachers' beliefs towards the nature of mathematics. The study was carried out using the exploratory mixed methods. The qualitative research design of the study was conducted with a single case study and the quantitative research design was carried out with a descriptive survey study. The participants of the qualitative part of the study are 53 senior pre-service mathematics teachers, selected by convenient sampling method. The quantitative part of the study comprises 499 participants, who are pre-service mathematics teachers, selected by convenient sampling method. The data in the qualitative part of the study were collected through a feedback form which has two open-ended questions. The analysis of qualitative data was conducted by means of semantic content analysis. The results of the qualitative analysis of the study revealed that the mathematical beliefs of pre-service teachers are divided into four categories: tool-oriented, aim-oriented, progress-oriented, and function-oriented mathematical beliefs. Scale items were written based on these four categories and other relevant scale items in the literature were not used at this stage. Validity-reliability studies, exploratory factor analysis, 27% upper and lower group comparisons, item-total correlation and Cronbach's Alpha values were calculated by applying the scale items obtained from this process to the pre-service teachers. The results of the study reveal a two-factor scale with a high validity and reliability.