A study on the estimation of underground rock petterns in Tolnaku village Kupang Regency has been conducted. The study aims to identify types of rock layers and to estimate the deph of each layer. Data was taken using geoelectricity method with Schlumberger configurasi while the data analysis was performed using Res2Dinv to obtain the real resistivity value. From the results, rocks foud in the research location are clay with resistivity being 1.1 – 27.6 (between 5 – 105 m), alluvium with resistivity being 10.0 – 79.4 (between 5 – 105 m), and limestone with resistivity being 50.0 - 1.817 (between 25–105 m). Key words: Geoelectric resistivity, Schlimberger, Res2Dinv.