Poly-vinylpyrrodione (PVP) protected Cu/Pd nanoparticles synthesized with citric complexing agent were developed as activator for electroless copper deposition in printed-circuit boards (PCBs) industry. Cu/Pd nanoparticles in different molar ratio were employed in electroless copper deposition and found that the catalytic activity was influenced not only by the amount of I'd content or particle size but also by the surface protected PVP layer. From the time-resolved electroless copper deposition, we suggested that the catalytic efficiency should be evaluated by both initial activity and the structure of deposited copper film. As a result, the Cu/Pd nanoparticles of molar ratio = 1/2 was found to have best catalytic activity which was comparable to traditional Pd/Sn or pure Pd activator. In regard to the most concerned stability issue of Cu-content system, a surprising slow galvanic corrosion of Cu was found when Cu/Pd nanoparticles were exposed to the open air. Besides, slightly oxidation of Pd was found after air-exposure. Surprisingly, these Cu/Pd colloids maintain part of activity and well suspension even after 6-month exposure, suggesting well long-term stability as activator. In short, Cu/Pd nanoparticles synthesized with citric complexing agent with high catalytic activity and long-term stability was a promising activator for electroless copper deposition. (C) 2008 Elsevier Ltd. All rights reserved.