We study the localization of protons in the core of neutron stars for ten realistic nuclear models that share a common behavior of nuclear symmetry energy which saturates and eventually decreases at high densities. This results in the low proton fraction of beta-stable neutron star matter. Protons form a small admixture in the neutron star core, which is localized at sufficiently high densities. For every model we calculate the density n_loc above which the localization effect is present. Our results indicate that localization occurs at densities above 0.5--1.0 fm^-3. The phase with localized protons occupies a spherical shell or a core region inside neutron stars which contains significant fraction of all nucleons. Proton localization is of great importance for astrophysical properties of neutron stars as it strongly affects transport coefficients of neutron star matter and can produce spontaneous magnetization in neutron stars.

PACS numbers: 21.65.+f, 97.60.Jd