The effect of academic skills acquired in the early period on future school success is indisputable. In this regard, it is important that pre-service teachers who are trained to be future teachers have appropriate content knowledge. The purpose of the current study is to examine the pedagogical content knowledge of in-service and pre-service pre-school teachers in - sub-dimensions of pre-school mathematics such as number, pattern, order, shape, spatial perception and comparison. In the current study, which was conducted using an explanatory mixed design, 439 pre-service and 73 in-service pre-school teachers took part in the quantitative section and 9 pre-service and 22 in-service pre-school teachers in the qualitative section. The Pedagogical Content Knowledge Scale in Preschool Mathematics and a semi-structured interview form were used to collect data. The results of the study revealed that the pedagogical content knowledge of the pre-service and in-service teachers is at a medium level. It was also observed that the pedagogical content knowledge of the in-service pre-school teachers varied significantly depending on the years of teaching experience and that the pedagogical content knowledge of the pre-service preschool teachers varied significantly depending on gender, grade level, academic achievement, having taken the Mathematics Education course and belief in the necessity of mathematics education in the pre-school period. It was also found that both the in-service and pre-service teachers consider mathematics education necessary in the pre-school period due to its importance to get ready for primary school education, the acquisition of basic mathematics skills and the existence of mathematics in life. Additionallyy, both groups mostly preferred activities based on numbers, counting, operations, patterns, matching and concrete life experiences.