Weathering grades and their depths are some of the most important geo-engineering properties determining the cost, efficiency and sustainability of the engineering projects. Weathering properties of the rocks should be clearly defined during the preliminary surveys of the studies on foundations, slopes etc. As weathering properties are heterogeneous and anisotropic more boreholes are needed to increase the accuracy of the interpretations of the subsurface. Electrical Resistivity Tomography (ERT) technique is used for different purposes to obtain faster and more economical data from wider area than drilling. Due to such specialities of ERT, the technique was used for determining the weathering properties of the pyroxenites and dunites outcropping in Bursa region. ERT studies were carried out in three lines. Two- of the lines were on the dunites and the other line on the pyroxenite. Dunites in this study were observed from unweathered to completely weathered stages, and the pyroxenites were observed from slightly to completely weathered stages. During ERT studies both dipole-dipole and Wenner configurations were deployed. According to the data obtained, inversion model sections were generated. These sections were evaluated regarding the changes in engineering properties of the dunites and pyroxenites. According to the evaluations, it is concluded that Wenner configuration especially for the dunites represents better resistivity distributions for the weathering properties.