In this study, we re-analyze geophysical survey data in order to image intermediate to deep geoelectric structure and to enhance understanding of subsurface structures in the region of South-Eastern part of Korea. This region in South Korea becomes geologically more important after an earthquake in Gyeongju (ML 5.8) in 2016, since it is the largest event among those which have been instrumentally recorded in South Korea. To obtain an image of geoelectric structures, we reprocess magnetotelluric (MT) sounding data, which were originally acquired during 2012~2017 in the region near south Gyeongju and north Ulsan for geothermal resources exploration. The area where MT sounding were performed includes the major faults zones, Yangsan, Milyang Moryang, and Ulsan Faults developed in this region, in NNE direction. The purpose of the MT surveys lies in delineating the extension of the major faults. The total number of MT measurement points are 67, and the frequency band of MT signal are ranging from 0.01 to 1,000 Hz. The strike directions of major faults are approximately NNE, so the 2D MT lines for interpretations are set up along 110 degree from North. The successive 2D inversions are done for TM mode and joint mode of TM and TE data. In addition, 3D inversion domain encompassing the whole area of MT stations are also performed to obtain detailed image of the area. We also recompile airborne magnetic data to compensate for geologic model. The geoelectric image clearly shows fault zone conductors and their extensions over the region and will help understand subsurface structure of major faults zone in South-Eastern part of South Korea.