The purpose of this research was to determine the pre-service primary mathematics teachers' competency of pedagogical content knowledge in mathematics. The data were collected by means of four open ended problems from the participation of 45 primary mathematics teacher candidates. Teacher candidates' responses were analyzed based on pre-determined criteria. According to findings it was found that having a deep understanding of mathematical knowledge was necessary but not sufficient to teach mathematics. This finding pointed out the connection between knowledge of mathematics and knowledge of mathematics teaching. It is suggested that primary mathematics teacher candidates should be educated both from "mathematics knowledge" and "pedagogical content knowledge" aspects. (Contains 2 figures and 4 tables.)