Effective mathematics teaching can be actualized only with correct use of the mathematical content language which comprises mathematical rules, concepts, symbols and terms. In this research, it was aimed to examine the mathematics prospective teachers' content language skills in some basic geometric concepts which are ray, angle, polygon, Pythagorean Theorem, area formula of trapezoid and surface area formula of the cone. Participants of the present study were constituted of third grade students in university. From results, it was determined that participants were not able to use the mathematical language adequately and usually not able to explain the concepts using symbols. It was also determined that there were some mistakes on the verbal level that the prospective teachers used to explain the concepts in the research.