The paper presents the results of 2D density modeling of gravity anomalies within the South Onega trough (South Karelia). The iterative algorithm of layering selection was applied in the model of layer-block structure of the earth’s crust. The primary parameters of the model were obtained based on geological, seismic and petrophysical data on the structure of the study region. The results of the investigation allowed us to determine the structure of the trough, identify the existence of two deep geological bodies and evaluate their form and size.