New Au@SnO₂ yolk?Cshell nanospheres have been successfully synthesized by using Au@SiO₂ nanospheres as sacrificial templates. This process is environmentally friendly and is based on hydrothermal shell-by-shell deposition of polycrystalline SnO₂ on spheriform Au@SiO₂nanotemplates. Au nanoparticles can be impregnated into the SnO₂nanospheres and the nanospheres show outer diameters of 110 nm and thicknesses of 15 nm. The possible growth model of the nanospheres is proposed. The gas sensing properties of the Au@SnO₂ yolk?Cshell nanospheres were researched and compared with that of the hollow SnO₂ nanospheres. The former shows lower operating temperature (210 °C), lower detection limit (5 ppm), faster response (0.3 s) and better selectivity. These improved sensing properties were attributed to the catalytic effect of Au, and enhanced electron depletion at the surface of the Au@SnO₂ yolk?Cshell nanospheres.