Colloidal Au-Ag alloy nanoparticles with various Ag/Au molar ratios were first prepared by a co-reduction method in P123 aqueous solution and characterized by UV-vis, TEM, and XPS. The prepared Au-Ag alloy nanoparticles were substantially stable and had comparable particle sizes (3-4 nm) for erobic oxidation kinetics of benzyl alcohol. The addition of Ag not only significantly enhanced the reaction rate but also increased the apparent activation energy (E-a) compared to that for monometallic Au nanocatalysts. The kinetics investigations indicated that on the pure Au sites, the oxidation of benzyl alcohol followed 1.5-order reaction kinetics, while on Au sites adjacent to Ag atoms, it followed 0.5-order reaction kinetics. The presence of Na2CO3 greatly improved the catalytic activity of Au-Ag nanocatalysts but decreased the selectivity to benzaldehyde. (C) 2013 Elsevier Inc. All rights reserved.