The general purpose of this study is to investigate the development of geometric thinking of elementary school mathematics teachers. To achieve this, the model of research is defined as a lesson study. The implementation process of the study was carried out with five mathematics teachers from different schools. Firstly, a five-week seminar process was carried out with teachers. As part of this process, the lesson study was explained with the theoretical framework of Geometric Habits of Mind and its practices were implemented. Then a lesson study was performed which took about three months. Data was collected by using multiple data collection tools and data analysis was carried out by using a video analysis model developed by Powell, Francisco, and Maher (2003). As a result of this study, geometric thinking of teachers has improved through the lesson study. During the process from the first lesson study to the seventh lesson study, we observed the improvement in the mathematical language used by teachers, their explanations, student questions in class, together with activities and problems produced by teachers based on the geometric habits of mind for the relevant concepts. In the instructional processes, we also observed the teachers considering and assessing these components and planning for and implementing them in the geometry lessons. After the lesson studies, teachers also considered the geometric habits in their own school settings and reflected on the instructional process through prepared activities and problems which were then identified.