Metal-oxide hybrid nanocatalysts with ultrathin oxide encapsulation can be a new platform to test the metal-support interaction. Metal nanoparticles (Ru, Rh, or Pt) capped with polymer/citrate were deposited on functionalized SiO2 and then an ultrathin layer of TiO2 was selectively coated on the SiO2 surface to prevent sintering and to provide high thermal stability while maximizing the metal-oxide interface for higher catalytic activity. Transmission electron microscopy studies confirmed that 2.1-2.3 nm metal nanoparticles were well dispersed and distributed throughout the surface of the 25 nm SiO2 nanoparticles, and that a 2 nm ultrathin TiO2 layer existed on the surface of the particles. The metal nanoparticles were still well exposed to the outer surface, thus allowing for surface characterization and catalytic activity. Even after calcination at 600 A degrees C, the structure and morphology of the hybrid nanocatalysts remained intact, confirming high thermal stability. The catalytic activities of the hybrid nanocatalysts with ultrathin oxide encapsulation (SiO2/M/TiO2, M = Pt, Rh, or Ru) were evaluated using the CO oxidation reaction. Hybrid nanocatalysts encapsulated by the ultrathin oxide layer allowed us to obtain high thermal stability and better exposure of the metal active sites for a strong metal-support interaction between the metals and the ultrathin TiO2.