Au core Pd shell (Au@Pd) nanoparticles with controllable size from 35 to 100 nm were prepared by chemical deposition, of Pd over pre-formed 12 nm Au seeds. Both transmission electron microscopy and LTV-visible spectroscopy studies confirmed the coreshell structure of the synthesized nanoparticles. The Au@Pd nanoparticles dispersed on a polished Pt electrode surface exhibit high surface-enhanced Raman scattering (SERS) effect for the adsorbed pyridine and SCN-. With the aid of the long-range effect of the electromagnetic (EM) enhancement created by the SERS-active Au core underneath the Pd shell, the good quality SERS spectra of adsorbates on the palladium metal overlayer can be obtained. Such kind of SERS-active substrate can be used as an alternative substrate to massive metals for investigating adsorption and reactions occurring on the Pd metal catalyst. (c) 2005 Elsevier B.V. All rights reserved.