Everyday problems become more complex in our lives. Individuals who start working life are expected to solve these complex problems. In order to solve these problems, it is necessary to encounter and practice before. Therefore, teachers should introduce their students with complex problems during education. The development of students' thinking skills is closely related to teachers' knowledge. The aim of the study is to determine graduate program science teacher’ level of system thinking in the explanation of respiratory subject. The study group of the study consisted of 16 teachers (6 Ph.D., 10 Master) who are attending a science teaching program in a state university in Istanbul in 2018-2019 academic year. Quantitative and qualitative data collection tools were used in the study. Respiratory system thinking test was used to collect quantitative data, and concept maps drawn by teachers were used as qualitative data collection tools. As a result of the quantitative data, it was determined that the system thinking levels of the teachers were at the level of practice-synthesis, 30% synthesis and 60% analysis. In the qualitative data analysis, it was found that while they were successful in identifying system components and establishing simple relationships between system components, they were not successful in defining dynamic relationships between system components and organizing system components within interactions.
respiration, system, complex concept, system thinking