The purpose of this study is to investigate seventh grade students’ mental models about global warming. 185 students of a secondary school participated to this study in 2012-2013 school year. To collect data “Global Warming Interview Form (GWIF) was administrated. The students were asked a number of open-ended questions about global warming. In this research, case study method was used, which is one of the qualitative method patterns. For the analysis of qualitative data, frequency analysis was used, which is a content analysis method. In the end of the research, it is found that most of the students relate their perception of “global warming” with the concepts of drought, glacial melting. Correspondingly it is indicated that students have unclear and complex mental model. It is also found that students’ knowledge level about global warming is not sufficient and their mental models are in low level. Hence it is suggested that teachers should include learning environments that take into account the level of reasoning and spatial thinking of the students and more detailed information and visual models of global warming in the curriculum.