Bimetallic nanoparticles with a Au-core/Pd-shell structure were prepared and successfully immobilized on a TiO2 surface using sonochemical method. When immobilizing the core/shell structured bimetallic nanoparticles with a Au/Pd molar ratio of 25/75, TiO2 showed the highest activity for the photochemical H-2 evolution from ethanol aqueous solution. The activities of other two types of photocatalysts with the same Au/Pd molar ratio, TiO2 immobilizing the mixture of Au and Pd monometallic nanoparticle, and TiO2 immobilizing Au/Pd random alloy nanoparticles wherein Au and Pd atoms homogeneously located, were also evaluated. The dependence of the photocatalytic activities on the nanostructures of the immobilized bimetals was confirmed. (C) 2009 Elsevier B.V. All rights reserved.