The aim of our research is to determine the change in the pedagogical content knowledge levels of the teachers on numbers in the period from their university education to their active teaching profession. The sample of the study is composed of a total of 210 people, 67 of whom are third grade pre-service mathematics teacher, 98 of whom are 4th grade pre-service mathematics teachers and 45 of whom are mathematics teachers who are working in various provinces of Turkey. As for the data collection tools of this research, “Mathematics Pedagogical Content Knowledge Test (MPCKT)” was used. Cross-sectional comparative study, which is among the descriptive research designs, was used in this research. It was observed that the secondary mathematics teachers’ levels of knowledge of understanding students and knowledge of instructional strategies, which constitute two sub-components of pedagogical content knowledge, exhibited development from their third-year in university to the period in which they carry out teaching profession.