Abstract Glass-like thermal conductivity is observed in (La 1− x Yb x ) 2Zr 2O 7 (1/6 ⩽ x ⩽ 1/3), which exhibits great potential as a high-temperature thermal barrier coating material. In the pyrochlore-type La 2Zr 2O 7, the large 16 c-site La 3+ is weakly bonded by its surrounding 48 f-site oxygen ions, and substitution of La 3+ with smaller and heavier Yb 3+ gives rise to a large atomic displacement parameter (ADP) of Yb 3+ which behaves as a “rattler”, as evidenced by the X-ray diffraction refinement. The localized “rattling” of Yb 3+ in the cation sublattice significantly scatters the heat-carrying phonons and lowers the thermal conductivity close to the amorphous limit in combination with the intrinsic oxygen vacancies in the anion sublattice. In contrast, substituting Yb 3+ with the larger La 3+ in Yb 2Zr 2O 7 does not result in as remarkable a decrease in the thermal conductivity as in Yb-doped La 2Zr 2O 7 due to the absence of rattling atoms. In this study, a resonant phonon scattering is proposed as a new approach to reduce the thermal conductivity of oxides which are important in various thermal engineering applications.