Content knowledge which is the most important source of the mathematicians  (Schoenfeld, 2010)  is the main component of the teacher proficiency (Grossman & Schoenfeld, 2005). Teachers' level of mathematical knowledge is the significant factor forming his pedagogical content knowledge (Baki, 2012). The aim of this study is to deal with mathematics knowledge of mathematics teaching students in the department of mathematics and science education. 32 freshman students were participated the research during the 2016-2017 Fall semester in Kırıkkale University School of Education. “Mathematics Knowledge Instrument” developed by Rakes (2010) in his Ph.D thesis was adaptated to the Turkish language applied to the students. While the instrument containing 17 questions was adapted to the Turkish,  total 14 questions were selected based on the learning fields of Probability (4 questions), Numbers and operations (4 question) and Algebra (6 questions) by taking into account the  Middle school (5-8 grade) mathematics curriculum. In the data collection instrument composed of multiple choice quesitons, students asked to marked the correct answer as well as to explain the reason of their choices. Data were analyzed by the criterion developed by the researchers. Students responses were analysed  by the correct/ false/ blank answer, sufficient explanations or operations and their types of error. According to the data analyses, students generaly response the questions correctly in the three learning fields. However, when they asked to explain the reason of their  answers they did not pose enogh explanations and it was seen that their missing explanations were mostly in the probability field. When students answers were classfied by error types, it was found that notation mistakes were mostly in numbers and operations learning filed while conceptual mistakes were mostly in the probability learning field.