Pt/Pd and Pt/Au bimetallic nanoparticles stabilized by octa(diacetic aminophenyl)silsesquioxanes (OAAPS) were prepared and used as catalysts for hydrogenation of phenyl aldehydes to phenyl alcohols with dihydrogen under mild conditions. Transmission electron microscopy (TEM), X-ray diffraction (XRD), and UV-vis absorption spectroscopy showed that nearly monodisperse nanoparticles having average diameters of 2.6 +/- 0.5 and 3.1 +/- 0.7 nm for Pt/Pd and Pt/Au bimetallic nanoparticles formed. The colloidal solution of the bimetallic nanoparticles stabilized by OAAPS is stable without precipitation for 3 months at room temperature since OAAPS can offer strong bonding to the bimetallic nanoparticles through the chelating effect. Pt/Pd bimetallic nanoparticles stabilized by OAAPS showed much higher catalytic activity for the hydrogenation of phenyl aldehydes to pheryl alcohols than their monometallic counterparts. The Pd atoms in Pt/Pd nanoparticles promoted the activity of the catalytic hydrogenation mainly through geometric and electronic effects. The bimetallic nanoparticles stabilized by OAAPS can be separated from the reaction system and reused by simply adjusting the pH of the colloidal solution. (C) 2007 Elsevier B.V. All rights reserved.