The purpose of this study is to investigate a group of prospective middle school mathematics teachers’ knowledge on the concept of angle through their concept maps created within a computer-based environment. To this end, 57 middle school future mathematics teachers were first introduced to Inspiration9 software which was developed to create concept map. The participants then were asked to create a concept map illustrating the concept of angle and relationships between the concepts by using Inspiration9. The findings revealed that when preparing concept maps, the prospective teachers were not able to establish significant relationships between the concepts in diagonal relations in terms of subject matter knowledge. On the other hand, the concept maps were found to be instrumental in conceptual understanding and in assessing the structural changes.