Gold catalysts nanometrically dispersed over Al2O3, ZrO2 and ZrO2/Al2O3 are prepared and tested in selective CO oxidation. XRD, DRS, Raman and in situ DRIFTS techniques are used to investigate the main causes of activity loss after long period storage, evaluating the physical-chemical properties of the fresh catalyst and after 2 years storage. Storing in darkness is not efficient to maintain the catalytic activity. The gold particle sizes increase 13-54% depending on the support. The auto-reduction of cationic gold nanoparticles causes the decrease of CO chemisorption capacity and hence a drastically decrease in the activity. (C) 2010 Elsevier B.V. All rights reserved.