The aim of this study was to determine the level of knowledge and mental models of secondary school students regarding the solar system. The study was performed with 65 eighth grade students attending a secondary school in a provincial center in northern Turkey. In this study, students were asked to draw the solar system, and to write the names of the planets in the proper order. Descriptive analysis was performed on the drawings and written descriptions provided by the students, with the data being evaluated based on five different levels previously used by Bartoszeck et al. (2008) and Uzunkayak (2009a; 2009b). Based on the study results, it was determined that the students lacked sufficient knowledge regarding the solar system, and that they possessed erroneous information regarding the order and sizes of the planets. In addition, none of the students were able to write down the eight planets of the solar system, which further illustrated their lack of knowledge on this subject.