The local structure around the oxide ions in LnO1.5-CeO 2 (Ln = La, Nd) was studied by using 17ONMR spectroscopy. Each spectrum of LnO1.5-CeO2 showed a broad peak due to a distribution of oxygen tetrahedra. From the peak separation, the relative numbers of oxygen tetrahedra, O[Ce]4, O[Ce]3[Ln], and O[Ce]2[Ln]2, were determined quantitatively. In the La2O3CeO2 system, the amounts of O[Ce] 4, O[Ce]3[Ln], and O[Ce]2[Ln]2 deviated from the calculated value for over 20 mol% La-doped ceria (LDC). The distribution of oxygen tetrahedra for LaO1.5CeO2 differed from those in LnO 1.5CeO2 (Ln = Nd, Y). These results suggest that the stability of the oxygen tetrahedra changes with the size of the doped ions.