NaNbO3:SrTiO3 interface nanolayers are studied by combining first-principles modeling and experimental approach. The nature of NaNbO3:SrTiO3 interface is investigated using density-functional theory calculations. Interface parameters are experimentally estimated using analysis of the dielectric response of SrTiO3 and NaNbO3 epitaxial films and NaNbO3:SrTiO3 superlattices. It is shown that NaNbO3:SrTiO3 interfaces can be approximated by dielectric nanolayers with thickness 1–2 nm and with temperature independent permittivity 25–55. Mechanism responsible for the nanolayer formation is the ionic charge mismatch between constituents.