One of the most ancient cultural heritages of Hungary is the fire tower located in the heart of Sopron city. With the passage of time, some renovation and reinforcement studies were required for the valuable structure. For this purpose, GPR based non-destructive geophysical surveys were carried out before and after cement injection in order to observe the changes within the structures of the walls, to understand the success of cement injection in the reinforcement studies, to find and to monitor the voids and possible cracks on the ancient walls and to find the proper places within the walls of the historical tower which were needed to be injected by cement. These surveys were applied during the preliminary stage of the structural monitoring project and during restoration of the four main parts of the fire tower's walls. Additionally, some GPR surveys were carried out before the steel was inserted into some parts of the walls and some units of the fire tower. After the cement injection process, it is realized that the reflections from the fractured and porous zones weakened or were lost as seen clearly in GPR data. Besides these, significant rises within the P-wave velocities were also observed. (C) 2014 Elsevier B.V. All rights reserved.