A domain structure in periodically poled stoichiometric LiNbO₃ was observed by confocal micro-Raman scanning spectroscopy. The 180°-domain, which is nominally invisible by Raman scattering due to equivalency of Raman selection rule for adjacent domains, was clearly visualized with a spatial resolution of 460 nm. At domain walls, an enhancement of Raman intensity was observed in optical modes that are closely related to the Nb–O bond, while there was no significant change in Li-ion related modes. Nb–O covalent bonds would be deformed by opposite ferroelectric displacements of ions across domain walls, to modify an electric polarizability of the Nb-ion related modes.