Ceria supported gold catalysts containing 0.1-5 wt.% gold are prepared by deposition-precipitation technique in which the precipitate is subjected to ultrasound treatment and aging in the parent solution at 65 degrees C for 2 h prior to filtration and drying. The catalysts are found to be very active for the room temperature oxidation of CO. Au/CeO2 catalyst containing as low as 1 wt.% Au is found to be a highly active catalyst for the room temperature oxidation of CO to CO2 with complete conversion of CO and specific activity up to 490 x 10(-4) mol(CO) s(-1) g(Au)(-1). The catalyst shows good stability and sustains its high activity for a prolonged period. Aging of the catalyst in the parent solution is found to be important in obtaining a highly active catalyst. The catalysts are characterized by XRD, SEM, TEM, XPS and TPR/TPD. TPR, TPD and XPS studies suggest that the active site for CO oxidation may be a combination of Au+-OH- and metallic gold in interface with reduced Ce3+ sites. In other words, the presence of highly dispersed gold particles in close contact with the ceria surface defects is vital for the superior performance of the catalyst. (c) 2005 Elsevier B.V. All rights reserved.