The aim of the present study was to investigate the nature of global argumentation structures of prospective middle school mathematics teachers in a technology enhanced environment. A qualitative case study was conducted with 8 participants from an Elementary Mathematics Education undergraduate program of one of the public universities in Ankara. Two implementations, 1 of which included 2 geometry tasks on triangles and another which included 2 geometry tasks based on circles, were conducted. Subsequently, global argumentation structures were revealed via data analysis. The findings indicated that the prospective middle school mathematics teachers resort frequently to simple global argumentation structures since their mathematical reasoning was insufficient. On the other hand, technology had a positive impact on argument construction and global argumentation structures of prospective middle school mathematics teachers. However, it was deduced that prospective middle school mathematics teachers need to be challenged on argumentation and about how to facilitate argumentation effectively in their future classroom experiences.