This study was carried out to reveal the mental models of the secondary school students from different grade levels regarding the concept of space. At the same time, within the context of the study, it was aimed to determine the factors playing a role in the construction of their concepts of space. The study employed the special case study design, one of the descriptive methods. The study was conducted in the spring term of the 2016-2017 school year and the sampling of the study is comprised of the students attending a private secondary school in a city located in the western region of Turkey. In the study, a data collection tool including four open-ended questions developed by the researchers to determine the students' mental models of the "space" was used. The collected data were analyzed by using descriptive statistical techniques. The findings of the study have revealed that the students mostly associate the concept of the space with the concepts of emptiness (53 students), infinity (50 students), planet (48 students) and star (28 students). These findings are also supported by the students' drawings and the Celestial Bodies Mental Model was found to be the model most frequently used by the students.