In this study, we report on the influence of support and gas atmosphere on the thermal stability of Au nanoparticles on oxidic supports. All samples were prepared with a modified impregnation method and have initial Au particle sizes in the range of 3-4 nm. We observed that in air, Au nanoparticles on SiO 2 and Al 2 O 3 are thermally much more stable than Au nanoparticles on TiO 2. For instance, upon treatment up to 700°C, on SiO 2 , Au particles grew from 4 to 6 nm while on TiO 2 from 3 to 13 nm. For Au nanoparticles on TiO 2 , growth is accelerated by oxidizing atmospheres and the presence of water and/or chloride. On nonreducible supports and in non-oxidizing atmosphere, the supported Au nanoparticles were remarkably stable. The insight into the growth of oxide-supported Au nanoparticles in reactive atmosphere offers an additional tool for a rational choice of a support for high-temperature gas-phase reactions involving gold nanocatalysts.