Many gold catalysts have been actively surveyed, but Au/SiO2 catalysts that are highly active for CO oxidation still remain evasive. In this work, bold nanoparticles well dispersed on Cab-O-Sil fumed SiO2 were prepared using Au(en)(2)Cl-3 (en = ethylenediamine) as the precursor, and found to be very active for CO oxidation below 0 degrees C. The catalyst pretreatment via reduction and calcination, effect of gold loading, post-treatment in acidic and basic media, catalyst deactivation, storage, regeneration, and effect of surface modification by other metal oxides were explored. The results provide new perspective on the activation and promotion of active Au/SiO2-based catalysts. (c) 2007 Elsevier B. V. All rights reserved.