Development of microelectronic devices is driven by a large demand for faster and smaller systems. In the near future, colossal permittivity in nanomaterials will play a key role in the advances of electronic devices. We report on “colossal” permittivity values achieved in dense ceramics displaying ultrafine grain size ranging from 70 nm to 300 nm. Relative permittivity values of ∼ 106 at 1 kHz (0.1 < tand < 0.7) were obtained for Ba0.95La0.05TiO3–x ceramics. The colossal effective permittivity is related to an interfacial polarization and is achieved in nanomaterials by the activation of a high number of carriers and their trapping at the interfaces. Polarization carriers involving Ti3+ polaron is proposed to be at the origin of the observed colossal permittivity. These results may have an important technological impact since these ceramics display ultrafine grain size opening a new route to the fabrication of very thin dielectric films.