Cr-rich shells are known to decrease the lattice misfit of Y-Ti-O nanoparticles and contribute to high thermal stability. In the present work, the formation of a Cr-rich shell on the Y2Ti2O7/Fe interface is studied via density functional theory and examined with electron microscopy analyses. The density functional theory calculation showed that Cr substitution in Y2Ti2O7 is not allowed. Instead, Cr is favorably segregated on the interface of the Fe site owing to the strong binding energy between Cr and O. Atom probe tomography observations confirmed the formation of a Cr shell at the interface between Y2Ti2O7 nanoparticles and the Fe matrix. Contrary to the density functional theory calculation, a considerable Cr concentration was detected inside the oxide. However, additional transmission electron microscopy observation of very coarse Y2Ti2O7 nanoparticles demonstrated that the Cr concentration is almost negligible inside the oxide, which is consistent with the calculated prediction.