Au@SnO2 core-shell nanoparticles (NPs) were synthesized by a microwave-assisted hydrothermal method. These NPs were characterized by electron microscopy, UV-visible spectroscopy and X-ray diffraction (XRD). Transmission electron microscope (TEM) images showed the formation Au@SnO2 core-shell NPs, where 12-15 nm Au NPs were covered with SnO2 shell layer. SnO2 shell thickness was controlled from 6 to 20 nm by repeated treatment with sodium stannate (Na2SnO3) solution. The surface plasmon resonance (SPR) peak of Au NPs was red-shifted (520-576.5 nm) with increasing shell thickness. XRD results confirmed the formation of the rutile phase of SnO2 with increasing crystallite size (7-11.6 nm) as shell thickness (6-20 nm) increased. The response of Au@SnO2 NPs for CO gas was increased with increasing shell thickness, and reached a maximum for 15 nm SnO2 shell. The response of Au@SnO2 core-shell NPs was higher than that of bare SnO2 as well as Au deposited on SnO2 NPs. Improved performance was attributed to the pronounced electronic sensitization, high thermal stability and low screening effect of Au NPs in Au@SnO2 core-shell NPs. The sensing mechanism of Au/SnO2 core-shell NPs for CO gas is also discussed. (C) 2015 Elsevier B.V. All rights reserved.