Four of the largest funeral tumuli located in the region of SW Thrace, Greece, were investigated through the use of geophysical techniques. These monumental mounds are found scattered all over Thrace and belong to a period spanning from the Late Bronze Age to the Roman period. Rescue excavations that have been carried out in a few of these tombs revealed a significant number of burials and finds, including funeral pyres, tomb architectural remnants and grave pits. Still, most of the tumuli do not contain any significant relics. Ground penetrating radar was systematically employed, among other techniques for the study of the tumuli in the region of Orestiada and Trigono. The goal of the geophysical campaign was to pinpoint the most prominent targets to be explored by future excavations. Controlled GPR experiments were carried out on the top of a tumulus at Elaphochori-Daphni, where excavations had revealed a medium sized stone built tomb. In Spilaion, shallow depth time slicing maps of the tumuli were combined together with the soil resistance maps of the neighboring hill, which showed evidence of a large circular feature. In the tumulus of Mikri Doxipara, time slicing techniques identified a recent war trench together with other candidate targets. All data were corrected taking into account the topography of the tumuli. Comparison of time slices produced by transects of different orientations showed a low degree of correlation, suggesting that the alignment of the antenas may play a critical factor in the GPR survey. Finally, time slices were also used for the production of 3-dimensional solid modeling of the tombs. In the case of the tumuli of Chelidonas-Ladi, the high resolution magnetic survey conducted after the removal of the bulk of the mound mapped the details of a neolithic settlement, located at the base level of the tomb.