The paper is aiming to determinate the extent of the north eastern arm of Kozłowicka buried valley on the grounds of own re search by means of electrical resistivity tomography- ERT and avail able archival researches. On the Hydro-geological map of Poland, Żyrardów sheet (Felter and Nowicki, 1998a, b) Kozłowicka buried valley was differentiated as an individual hydro-geological unit. The results of the anal y sis show that the ex tent of the structure, defined by its up per boundary, differs significantly from the one suggested on the sheet of Hydrogeological map of Poland. Since there was no data avail able in the north eastern part of the dis cussed arm of Kozłowicka buried valley, the northern boundary was defined only based on avail able geoelectrical sounding profiles (Czerwiñska, 1988; Topolewska, 2015). In order to confirm suggested solution, geoelectrical re search by means of electrical resistivity tomography (ERT) was con ducted. The measurements were per formed along 3 pro files located in the area of interest. The authors would like to point out the need of the us age of ERT in map ping and studying buried structures that might be ground water reservoirs. As a result, one obtains quasi-continuous image of electrical resistivity of the subsurface. Due to the contrast of electrical properties of sediments, it is possible to determine upper and bottom surfaces of buried structures, formed within glacial deposits.