Recent techniques of 3D geological models building present an innovative approach to integrated subsurface mapping of geological structures. Multiple sources of geological and geophysical data have been used in complex 3D modeling from both digital databases as well as analogue archives. Structural framework of the model supplemented with lithological and petrophysical data discretized in spatial grids is used for resources assessment and modeling of geological and hydrogeological processes. The 3D geological model of the Łanięta salt diapir has been developed as a case study for refinement of known structure and lithological variation of the salt dome with use of borehole data, cross sections and 2D seismic interpretation as well as petrophysical and geochemical analysis. The study has been focused on application of the geologically-constrained 3D geophysical inversion of gravity data for delineation of undrilled parts of the structure. The free-air correction of gravity data have been used for modeling of the structure from the terrain surface down to the depth of 1 km below sea level. Both regional and local gravity surveys were used in two steps approach. The low resolution regional model has been created for 3D trend model of density distribution in the first step. It was followed by the high resolution, detailed inversion of local gravity data. The 3D inversion constrained by borehole control points presents density variation of modeled structure. A significant challenge of presented approach of gravity inversion is an adequate differentiation of density in the salt diapir. The delineation of large density contrast of halite and anhydrite rock in the highly deformed internal diapir structures is problematic and it depends mostly on available borehole or seismic data on lithological succession and spatial distribution.