This is a quantitative study to develop a valid and reliable scale in order to determine mathematical thinking skills of mathematics teachers and to investigate the thinking skills of mathematics teachers in terms of various variables by means of the developed scale. In this context, the study was conducted on two different sample groups. The first study was conducted with 469 mathematics teachers during the development of the scale, and the second study was conducted with 190 teachers to test the developed scale. In the development process of the scale, exploratory factor analysis, confirmatory factor analysis and Cronbach Alpha internal consistency coefficient and Guttman Split Half values reliability calculations were performed. As a result of the analysis, the total variance percentage of the 17 items, which was composed of four factors, was 56.90%. The model obtained as a result of confirmatory factor analysis was acceptable. The Cronbach Alpha internal consistency coefficient for the whole scale was.79. The results of this study show that a valid and reliable scale was developed to determine mathematical teachers' mathematical thinking skills. In addition, through the developed scale, it was obtained that mathematics teachers' thinking skills differed according to the type of school they graduated and professional seniority.