The resistivity method in geophysics is used to solve various geological and engineering problems. Recently, this non-destructive method has been used on trees to investigate possible infections within the trunks by scanning resistivity variations. In this study, the electrical resistivity method has been aimed to be applied on various trees in Istanbul, Turkey to test whether the method applies to trees via regular resistivity measurement devices used in geophysics. Firstly, a multi-channel resistivity device, that is designed to automatically take measurements on the ground, is modified to carry out the measurements on trees. The measured data are processed using two different approaches. The first approach is to prepare a program in MATLAB, which is capable of adapting measurement points into a circular profile via interpolation. The data processed with this program are then gridded to prepare resistivity contour slices. The detection and handling of faulty measurements are discussed briefly in this section. The second approach is to use an open-source electrical tomography program (BERT V2) to apply inversion to the collected resistivity data. Finally, all the results and conclusions are interpreted considering the resistivity distribution within tree trunks, including sample slices from two trees that are known to have defected beforehand. As a conclusion of our studies, we have found that a regular resistivity measurement device used in earth sciences is applicable to an extent on trees to investigate possible defects within their trunks.