Mind maps that contain visual and verbal elements can be thought of as an effective graphical tool that can be used to reveal the existing knowledge, opinions and perceptions of individuals about a concept through mental association. In this study, the aim was to determine the mental models of middle school students related to science by using mind maps in terms of their gender and grade levels. 104 middle school students who were studying at different grade levels participated in the study. The study takes the form of a case study supported by qualitative data. First of all, students were given training on how to make mind maps, and sample implementations were carried out. Later, students were asked to prepare a mind map about the concept of science. Students' mind maps were first scored by experts by taking into consideration the evaluation criteria with regard to mind maps. In the data analysis process, each mind map was examined by using a descriptive analysis technique, while the frequency and percent values of the most common expressions were calculated. The results of the analyses revealed that the students' mind maps scores did not differ significantly in terms of their gender. It was concluded that the fifth grade students' mind map scores were significantly lower than those of other grade students. Thematic analyses showed that students mostly associate science with technology, and offer more examples of natural sciences in mind maps.