The site-selective spectroscopy has been applied on YSZ and Y3+-doped CeO2 system, which are typical oxygen ion conductor. Small amount of Eu3+ ions are introduced into these materials as optically active centers. It is found that there are three different sites for Eu3+ ions in YSZ, where the site symmetry is much lower than C2v. The luminescence spectra observed under site-selective excitation are quite similar to those observed in glass materials. In Y3+-doped CeO2 system, luminescence bands from three different sites of Eu3+ ions are observed by the site-selective spectroscopy. One of these bands is attributed to the luminescence from Eu3+ ions at Oh symmetry site.