Gold-based nanostructures with well-defined morphologies and hollow interiors have significant potential as a versatile platform for various plasmonic applications including biomedical diagnostics and sensing. In this study, we report the synthesis of Au@Ag core-shell nanocrystals with perfect octahedral shapes and tunable edge lengths via seeded growth. These nanocrystals were then oxidatively carved into yolk-shell nanocages with a retained octahedral morphology. The increase in octahedral edge length and volume of the interior hollow cavity synergistically leads to a red-shift of the LSPR peak. As a result, the optimized Au@AuAg yolk-shell octahedral nanocages showed a remarkable temperature increase of 23 °C upon 15 min irradiation of an 808 nm laser at a power density of 1 W cm-2. This study provides a feasible strategy for creating octahedral AuAg nanostructures with tunable sizes and hollow interiors and validates their promising use in NIR photothermal conversion.