We applied density-functional theory to investigate the CO oxidation catalyzed by the Au-38, Au-32/Pd-6, Pd-32/Au-6 and Pd-38 nanoparticles. Our calculations show that the formation of peroxo-type (OOCO) complex on Au and Au-shell/Pd-core nanoparticles is more favorable than that on Pd and Pd-shell/Au-core nanoparticles, while the cleavage of the O-O bond of -OOCO- intermediate occurs more easily on Pd and Pd-shell/Au-core nanoparticles. Compared to Au(111) and Au(321) surfaces, the [Pd](Au) and/or [Au](Pd) core-shell nanoparticles are predicted to show intrinsically more reactivity for CO oxidation. (C) 2012 Elsevier B. V. All rights reserved.