This study aims to define the depths, size, shape, and lateral extents of walls of the foundation of the Hagios Georgios Church by using ground-penetrating radar (GPR) as only some of its surrounding walls are currently on the surface nowadays. According to the literature, some restoration should be performed on its walls to prevent the complete demolishment of the extant walls of the church. Similar restorations of historical buildings have previously been approved without considering the foundations of these structures because excavation cannot normally be performed on such buildings. In these cases, some problems such as collapse and demolition of the structures may occur in historical buildings. Before the restoration of such historical buildings, the position of the structural foundations may be determined using GPR, which is a non-invasive technique that can give high-resolution results to address these problems. GPR data were acquired using by a Mala GPR system with 250 MHz and 800 MHz shielded antennas on 28 profiles in this study. Amplitude slice maps and 2D/3D views were generated after basic processing steps applied the data using Reflexw software. When interpreted, the results did not detect any void (or traces located in the lower floors of the ground) under the ground in the investigation site. Some parts of the high amplitude on 2D/3D views and slice maps also showed that some reflections have different shapes/sizes. It has been thought that these reflections originate from collapsed building stone (rubble, debris and freestone) remaining underground due to several causes. Finally, traces of the high amplitude identified the collapsed foundation of the walls and columns in the subsurface and the foundation of the undamaged wall of the church, which have been identified on slice maps.