Abstract: Bimetallic nanoparticle (NP) catalysts have attracted long-standing attentions for their wide applications in a broad range of chemical reactions. Their catalytic performance tightly relies on the structure of bimetallic NPs. Atomic-level understanding of their structural thermostability is of great importance for developing advanced bimetallic catalysts with high stability. Here we precisely fabricated Au@Pt and Au@Pd core-shell catalysts on a SiO₂ support with an identical Au core size of ~5.1 nm and a similar shell thickness of ~2 monolayers via selective atomic layer deposition. Spectroscopic characterizations were employed to compare their structural thermostability at elevated temperatures in a hydrogen reducing atmosphere. We revealed that the Au@Pt/SiO₂ core-shell catalyst exhibited a considerably higher structural thermostability against atom inter-diffusion to alloys than that of Au@Pd/SiO₂. Meanwhile, these two catalysts both preserved the particle size without any visible aggregation even after reduction at 550 ℃. Higher structural thermostability of Au@Pt/SiO₂ core-shell catalyst might mainly stem from the distinctly higher melting point of Pt shell and their relatively smaller Au-Pt lattice mismatch. Such direct comparison of the structural thermostability of two different core-shell catalysts but with identical structures provides a valuable insight into the nature of thermodynamic behavior of bimetallic NPs at elevated temperatures.