Atomically dispersed precious metals on oxide supports have recently become increasingly interesting catalytic materials. Nonetheless, their non-trivial preparation and limited thermal and environmental stability constitutes an issue for their potential applications. Here we demonstrate that an oxygen plasma pre-treatment of the ceria (CeO 2 ) surface serves to anchor Pt single atoms, making them active and resistant towards sintering in the CO oxidation reaction. Through a combination of experimental results obtained on well-defined CeO 2 films and theory, we show that the O 2 plasma causes surface nanostructuring and the formation of surface peroxo (O 2 2- ) species, favoring the uniform and dense distribution of isolated strongly bonded Pt 2+ atoms. The promotional effect of the plasma treatment was further demonstrated on the powder Pt/CeO 2 catalysts. We believe that plasma functionalization can be applied to other metal/oxide systems to achieve tunable and stable catalysts with a high density of active sites.